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Document And Entity Information - shares	9 Months Ended
Document And Entity Information - shares	Sep. 30, 2011	Oct. 28, 2011
Document And Entity Information
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2011
Document Fiscal Year Focus	2011
Document Fiscal Period Focus	Q3
Trading Symbol	swx
Entity Registrant Name	SOUTHWEST GAS CORP
Entity Central Index Key	0000092416
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		45,911,371

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2011	Dec. 31, 2010
Utility plant:
Gas plant	$ 4,667,840	$ 4,569,105
Less: accumulated depreciation	(1,614,486)	(1,535,429)
Acquisition adjustments, net	1,136	1,271
Construction work in progress	106,389	37,489
Net utility plant	3,160,879	3,072,436
Other property and investments	178,546	134,648
Restricted cash	37,783	37,781
Current assets:
Cash and cash equivalents	19,836	116,096
Accounts receivable, net of allowances	119,576	147,605
Accrued utility revenue	31,300	64,400
Income taxes receivable, net	7,688	21,514
Deferred income taxes	24,640	8,046
Deferred purchased gas costs		356
Prepaids and other current assets	83,604	87,877
Total current assets	286,644	445,894
Deferred charges and other assets	275,385	293,434
Total assets	3,939,237	3,984,193
Capitalization:
Common stock, $1 par (authorized - 60,000,000 shares; issued and outstanding - 45,901,110 and 45,599,036 shares)	47,531	47,229
Additional paid-in capital	817,035	807,885
Accumulated other comprehensive income (loss), net	(39,437)	(30,784)
Retained earnings	363,125	343,131
Total Southwest Gas Corporation equity	1,188,254	1,167,461
Noncontrolling interest	(808)	(465)
Total equity	1,187,446	1,166,996
Long-term debt, less current maturities	936,857	1,124,681
Total capitalization	2,124,303	2,291,677
Current liabilities:
Current maturities of long-term debt	221,102	75,080
Accounts payable	99,599	165,536
Customer deposits	84,459	86,891
Accrued general taxes	40,313	40,438
Accrued interest	19,553	20,162
Deferred purchased gas costs	93,652	123,344
Other current liabilities	122,985	85,510
Total current liabilities	681,663	596,961
Deferred income taxes and other credits:
Deferred income taxes and investment tax credits	505,409	466,628
Taxes payable	929	1,234
Accumulated removal costs	227,000	211,000
Other deferred credits	399,933	416,693
Total deferred income taxes and other credits	1,133,271	1,095,555
Total capitalization and liabilities	$ 3,939,237	$ 3,984,193

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2011	Dec. 31, 2010
Condensed Consolidated Balance Sheets
Common stock, par	$ 1	$ 1
Common stock, authorized	60,000,000	60,000,000
Common stock, issued	45,901,110	45,599,036
Common stock, outstanding	45,901,110	45,599,036

Condensed Consolidated Statements Of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Operating revenues:
Gas operating revenues	$ 195,647	$ 213,893	$ 1,022,914	$ 1,133,671	$ 1,401,150	$ 1,561,644
Construction revenues	156,945	93,790	346,623	228,588	436,499	299,420
Total operating revenues	352,592	307,683	1,369,537	1,362,259	1,837,649	1,861,064
Operating expenses:
Net cost of gas sold	67,165	81,303	468,026	581,294	622,907	779,911
Operations and maintenance	89,087	86,746	268,745	260,386	363,302	352,047
Depreciation and amortization	50,341	47,582	148,618	142,438	196,643	189,368
Taxes other than income taxes	10,585	10,006	30,750	29,388	40,231	38,826
Construction expenses	134,161	81,862	305,242	202,806	380,240	264,510
Total operating expenses	351,339	307,499	1,221,381	1,216,312	1,603,323	1,624,662
Operating income	1,253	184	148,156	145,947	234,326	236,402
Other income and (expenses):
Net interest deductions	(17,307)	(19,266)	(52,621)	(56,444)	(71,854)	(75,044)
Net interest deductions on subordinated debentures				(1,912)		(3,845)
Other income (deductions)	(8,087)	6,715	(6,814)	1,038	(4,002)	2,964
Total other income and (expenses)	(25,394)	(12,551)	(59,435)	(57,318)	(75,856)	(75,925)
Income (loss) before income taxes	(24,141)	(12,367)	88,721	88,629	158,470	160,477
Income tax expense (benefit)	(8,394)	(7,403)	32,101	30,126	56,900	55,946
Net income (loss)	(15,747)	(4,964)	56,620	58,503	101,570	104,531
Net income (loss) attributable to noncontrolling interest	(106)	(141)	(343)	(389)	(378)	(753)
Net income (loss) attributable to Southwest Gas Corporation	$ (15,641)	$ (4,823)	$ 56,963	$ 58,892	$ 101,948	$ 105,284
Basic earnings (loss) per share	$ (0.34)	$ (0.11)	$ 1.24	$ 1.30	$ 2.23	$ 2.33
Diluted earnings (loss) per share	(0.34)	(0.11)	1.23	1.29	2.21	2.31
Dividends declared per share	$ 0.2650	$ 0.2500	$ 0.7950	$ 0.7500	$ 1.0450	$ 0.9875
Average number of common shares outstanding	45,881	45,447	45,837	45,354	45,766	45,262
Average shares outstanding (assuming dilution)			46,264	45,756	46,203	45,657

Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
CASH FLOW FROM OPERATING ACTIVITIES:
Net income	$ 56,620	$ 58,503	$ 101,570	$ 104,531
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	148,618	142,438	196,643	189,368
Deferred income taxes	27,490	18,946	58,655	24,489
Changes in current assets and liabilities:
Accounts receivable, net of allowances	28,029	73,005	(34,859)	1,061
Accrued utility revenue	33,100	40,100	300	600
Deferred purchased gas costs	(29,336)	62,543	(58,866)	49,651
Accounts payable	(65,937)	(88,196)	28,939	3,820
Accrued taxes	13,396	(8,644)	6,800	29,085
Other current assets and liabilities	14,829	12,807	14,917	1,650
Gains on sale	(1,960)	(694)	(2,813)	(1,766)
Changes in undistributed stock compensation	4,278	3,863	4,844	4,389
AFUDC and property-related changes	(619)	(693)	(871)	(963)
Changes in other assets and deferred charges	7,534	(4,938)	210	(9,365)
Changes in other liabilities and deferred credits	8,291	6,786	(15,969)	6,043
Net cash provided by operating activities	244,333	315,826	299,500	402,593
CASH FLOW FROM INVESTING ACTIVITIES:
Construction expenditures and property additions	(263,626)	(151,417)	(327,648)	(196,864)
Change in restricted cash	(2)	11,990	(4)	(37,779)
Changes in customer advances	(4,764)	317	(5,911)	2,519
Miscellaneous inflows	3,803	2,304	5,574	4,788
Miscellaneous outflows	(2,719)	(2,800)	(2,719)	(2,853)
Net cash used in investing activities	(267,308)	(139,606)	(330,708)	(230,189)
CASH FLOW FROM FINANCING ACTIVITIES:
Issuance of common stock, net	4,728	7,475	8,351	11,854
Dividends paid	(35,760)	(33,455)	(47,151)	(44,134)
Interest rate swap settlement			(11,691)
Issuance of long-term debt, net	212,812		336,772	49,834
Retirement of long-term debt	(275,065)	(3,301)	(275,091)	(3,632)
Redemption of subordinated debentures		(100,000)		(100,000)
Change in credit facility	20,000	(92,400)	20,000	(99,300)
Net cash provided by (used in) financing activities	(73,285)	(221,681)	31,190	(185,378)
Change in cash and cash equivalents	(96,260)	(45,461)	(18)	(12,974)
Cash and cash equivalents at beginning of period	116,096	65,315	19,854	32,828
Cash and cash equivalents at end of period	19,836	19,854	19,836	19,854
Supplemental information:
Interest paid, net of amounts capitalized	50,809	57,454	80,355	75,768
Income taxes paid (received)	$ (13,714)	$ 18,505	$ (13,019)	$ 2,017

Nature Of Operations And Basis Of Presentation

9 Months Ended

Sep. 30, 2011

Nature Of Operations And Basis Of Presentation

Nature Of Operations And Basis Of Presentation

Note 1 – Nature of Operations and Basis of Presentation

Nature of Operations. Southwest Gas Corporation and its subsidiaries (the "Company") are composed of two segments: natural gas operations ("Southwest" or the "natural gas operations" segment) and construction services. Southwest is engaged in the business of purchasing, distributing, and transporting natural gas in portions of Arizona, Nevada, and California. The public utility rates, practices, facilities, and service territories of Southwest are subject to regulatory oversight. The timing and amount of rate relief can materially impact results of operations. Natural gas sales are seasonal, peaking during the winter months; therefore, results of operations for interim periods are not necessarily indicative of results for a full year. Variability in weather from normal temperatures, primarily in Arizona, can materially impact results of operations. Natural gas purchases and the timing of related recoveries can materially impact liquidity. NPL Construction Co. ("NPL" or the "construction services" segment), a wholly owned subsidiary, is a full-service underground piping contractor that provides utility companies with trenching and installation, replacement, and maintenance services for energy distribution systems.

Basis of Presentation. The condensed consolidated financial statements included herein have been prepared by the Company, without audit, pursuant to the rules and regulations of the Securities and Exchange Commission (the "SEC"). Certain information and footnote disclosures normally included in financial statements prepared in accordance with generally accepted accounting principles ("GAAP") have been condensed or omitted pursuant to such rules and regulations. The preparation of the condensed consolidated financial statements requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expense during the reporting period. Actual results could differ from those estimates. In the opinion of management, all adjustments, consisting of normal recurring items and estimates necessary for a fair presentation of results for the interim periods, have been made. It is suggested that these condensed consolidated financial statements be read in conjunction with the consolidated financial statements and the notes thereto included in the 2010 Annual Report to Shareholders, which is incorporated by reference into the 2010 Form 10-K, and the first and second quarter 2011 reports on Form 10-Q.

Intercompany Transactions. NPL recognizes revenues generated from contracts with Southwest (see Note 3 below). Accounts receivable for these services are presented in the table below (thousands of dollars):


	September 30, 2011		December 31, 2010

Accounts receivable for NPL services	$	13,680	$	8,111

The accounts receivable balance, revenues, and associated profits are included in the condensed consolidated financial statements of the Company and were not eliminated during consolidation in accordance with accounting treatment for rate-regulated entities.

Other Income (Deductions). The following table provides the composition of significant items included in Other income (deductions) on the consolidated statements of income (thousands of dollars):


	Three Months Ended						Nine Months Ended						Twelve Months Ended
	September 30						September 30						September 30
	2011			2010			2011			2010			2011			2010

Change in COLI policies	$	(6,700	)	$	7,750		$	(1,900	)	$	5,620		$	2,250		$	7,223
Interest income		118			49			308			127			375			154
Pipe replacement costs		(1,266	)		(927	)		(3,113	)		(3,918	)		(4,218	)		(4,305	)
Miscellaneous income and (expense)		(239	)		(157	)		(2,109	)		(791	)		(2,409	)		(108	)

Total other income (deductions)	$	(8,087	)	$	6,715		$	(6,814	)	$	1,038		$	(4,002	)	$	2,964

Reflected in the table above is the change in cash surrender values of company-owned life insurance ("COLI") policies (including net death benefits recognized). These life insurance policies on members of management and other key employees are used by Southwest to indemnify itself against the loss of talent, expertise, and knowledge, as well as to provide indirect funding for certain nonqualified benefit plans. Current tax regulations provide for tax-free treatment of life insurance (death benefit) proceeds. Therefore, the change in the cash surrender value components of COLI policies, as they progress toward the ultimate death benefits, is also recorded without tax consequences.

Reclassifications. A reclassification between two miscellaneous operating cash flow categories was made to the prior year's financial information to present it on a basis comparable with the current year's presentation with no impact on net cash provided by operating activities.

Out-of-Period Adjustment. In September 2011, the Company identified an isolated error in a regulatory deferral mechanism that overstated revenues by $3.7 million for periods prior to the third quarter of 2011. Management concluded the error was not material to any individual prior interim or annual period (or to the current annual period) and, therefore, the error was corrected during the third quarter of 2011. The effect was a decrease in revenues and regulatory assets of $3.7 million, of which $2.9 million pertains to years prior to 2011.

Recently Issued Accounting Standards Updates. In May 2011, the Financial Accounting Standards Board ("FASB") issued the update "Fair Value Measurement (Topic 820) Amendments to Achieve Common Fair Value Measurement and Disclosure Requirements in U.S. GAAP and IFRSs." The amended guidance includes several new fair value disclosure requirements, including, among other things, information about transfers between Level 1 and Level 2 of the fair value hierarchy, enhanced information about valuation techniques and unobservable inputs used in Level 3 fair value measurements, and a narrative description of Level 3 measurements' sensitivity to changes in unobservable inputs. For the Company, the update is effective prospectively beginning January 2012. The adoption of the update is not expected to significantly impact the disclosures of the Company.

In June 2011, the FASB issued the update "Comprehensive Income (Topic 220) Presentation of Comprehensive Income" which eliminates the current option to report the components of other comprehensive income in the statement of changes in equity. An entity will have the option to present the total of comprehensive income, the components of net income, and the components of other comprehensive income either in one continuous statement of comprehensive income or in two separate but consecutive statements. The update includes no changes to the components that are recognized in net income or other comprehensive income under current U.S. GAAP. The provisions of the update are effective for the Company beginning January 1, 2012 (however, early adoption is permitted). The Company is evaluating the update to determine which presentation option to adopt and the timing of adoption.

In September 2011, the FASB issued the update "Intangibles – Goodwill and Other (Topic 350) Testing Goodwill for Impairment." The update is intended to simplify how entities test goodwill for impairment. The update permits an entity to first assess qualitative factors to determine whether it is "more likely than not" that the fair value of a reporting unit is less than its carrying amount (including goodwill) as a basis for determining whether it is necessary to perform the two-step goodwill impairment test described in Topic 350. The more-likely-than-not threshold is defined as having a likelihood of more than 50%. The provisions of the update are effective for the Company beginning January 1, 2012 (however, early adoption is permitted). The adoption of the update is not expected to impact the Company's financial position or results of operations.

- Definition

The entire disclosure for organization, consolidation and basis of presentation of financial statements disclosure.

+ References

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+ Details

Components Of Net Periodic Benefit Cost

9 Months Ended

Sep. 30, 2011

Components Of Net Periodic Benefit Cost

Components Of Net Periodic Benefit Cost

Note 2 – Components of Net Periodic Benefit Cost

Southwest has a noncontributory qualified retirement plan with defined benefits covering substantially all employees and a separate unfunded supplemental retirement plan ("SERP") which is limited to officers. Southwest also provides postretirement benefits other than pensions ("PBOP") to its qualified retirees for health care, dental, and life insurance.


	Qualified Retirement Plan
	Period Ended September 30,
	Three Months						Nine Months						Twelve Months
	2011			2010			2011			2010			2011			2010
(Thousands of dollars)
Service cost	$	4,431		$	4,233		$	13,293		$	12,699		$	17,526		$	16,546
Interest cost		9,319			8,904			27,957			26,711			36,860			35,343
Expected return on plan assets		(10,028	)		(9,135	)		(30,085	)		(27,404	)		(39,219	)		(36,209	)
Amortization of net loss		3,587			2,620			10,761			7,859			13,380			8,922

Net periodic benefit cost	$	7,309		$	6,622		$	21,926		$	19,865		$	28,547		$	24,602


	SERP
	Period Ended September 30,
	Three Months						Nine Months						Twelve Months
	2011			2010			2011			2010			2011			2010
(Thousands of dollars)
Service cost	$	54		$	93		$	163		$	279		$	256		$	327
Interest cost		441			511			1,324			1,533			1,836			2,050
Amortization of net loss		158			289			473			867			761			1,095

Net periodic benefit cost	$	653		$	893		$	1,960		$	2,679		$	2,853		$	3,472


	PBOP
	Period Ended September 30,
	Three Months						Nine Months						Twelve Months
	2011			2010			2011			2010			2011			2010
(Thousands of dollars)
Service cost	$	215		$	214		$	644		$	642		$	858		$	824
Interest cost		658			623			1,974			1,869			2,596			2,461
Expected return on plan assets		(595	)		(523	)		(1,785	)		(1,569	)		(2,309	)		(1,970	)
Amortization of transition obligation		217			216			650			650			867			867
Amortization of net loss		147			122			442			366			565			475

Net periodic benefit cost	$	642		$	652		$	1,925		$	1,958		$	2,577		$	2,657

- Definition

Tabular disclosure of one or more of the entity's defined benefit pension plans or one or more other defined benefit postretirement plans, separately for pension plans and other postretirement benefit plans including the entity's schedule of fair value of plan assets for defined benefit or other postretirement plans.

+ References

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+ Details

Segment Information

9 Months Ended

Sep. 30, 2011

Segment Information

Segment Information

Note 3 – Segment Information

The following tables present revenues from external customers, intersegment revenues, and segment net income (thousands of dollars):


	Natural Gas Operations			Construction Services		Total
Three months ended September 30, 2011
Revenues from external customers	$	195,647		$	122,696	$	318,343
Intersegment revenues		-			34,249		34,249

Total	$	195,647		$	156,945	$	352,592

Segment net income (loss)	$	(25,566	)	$	9,925	$	(15,641	)


Three months ended September 30, 2010
Revenues from external customers	$	213,893		$	76,125	$	290,018
Intersegment revenues		-			17,665		17,665

Total	$	213,893		$	93,790	$	307,683

Segment net income (loss)	$	(8,813	)	$	3,990	$	(4,823	)


Nine months ended September 30, 2011
Revenues from external customers	$	1,022,914		$	280,635	$	1,303,549
Intersegment revenues		-			65,988		65,988

Total	$	1,022,914		$	346,623	$	1,369,537

Segment net income	$	42,648		$	14,315	$	56,963


Nine months ended September 30, 2010
Revenues from external customers	$	1,133,671		$	183,875	$	1,317,546
Intersegment revenues		-			44,713		44,713

Total	$	1,133,671		$	228,588	$	1,362,259

Segment net income	$	52,403		$	6,489	$	58,892


Twelve months ended September 30, 2011
Revenues from external customers	$	1,401,150		$	353,973	$	1,755,123
Intersegment revenues		-			82,526		82,526

Total	$	1,401,150		$	436,499	$	1,837,649

Segment net income	$	81,627		$	20,321	$	101,948


Twelve months ended September 30, 2010
Revenues from external customers	$	1,561,644		$	241,575	$	1,803,219
Intersegment revenues		-			57,845		57,845

Total	$	1,561,644		$	299,420	$	1,861,064

Segment net income	$	96,074		$	9,210	$	105,284

- Definition

The entire disclosure for reporting segments including data and tables. Reportable segments include those that meet any of the following quantitative thresholds a) it's reported revenue, including sales to external customers and intersegment sales or transfers is 10 percent or more of the combined revenue, internal and external, of all operating segments b) the absolute amount of its reported profit or loss is 10 percent or more of the greater, in absolute amount of 1) the combined reported profit of all operating segments that did not report a loss or 2) the combined reported loss of all operating segments that did report a loss c) its assets are 10 percent or more of the combined assets of all operating segments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 131
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8981-108599

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 35
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8984-108599

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 42
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e9054-108599

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 40
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e9031-108599

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 31
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8924-108599

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8538-108599

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
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-Paragraph 30
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8906-108599

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 41
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e9038-108599

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-Publisher FASB
-Name Accounting Standards Codification
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-Publisher FASB
-Name Accounting Standards Codification
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-Name Accounting Standards Codification
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
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-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8380-108599

Reference 14: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
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-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8595-108599

Reference 15: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
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-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8933-108599

+ Details

Derivatives And Fair Value Measurements

9 Months Ended

Sep. 30, 2011

Derivatives And Fair Value Measurements

Derivatives And Fair Value Measurements

Note 4 – Derivatives and Fair Value Measurements

Derivatives. In managing its natural gas supply portfolios, Southwest has historically entered into fixed- and variable-price contracts, which qualify as derivatives. Additionally, Southwest utilizes fixed-for-floating swap contracts ("Swaps") to supplement its fixed-price contracts. The fixed-price contracts, firm commitments to purchase a fixed amount of gas in the future at a fixed price, qualify for the normal purchases and normal sales exception that is allowed for contracts that are probable of delivery in the normal course of business and are exempt from fair value reporting. The variable-price contracts have no significant market value. The Swaps are recorded at fair value.

The fixed-price contracts and Swaps are utilized by Southwest under its volatility mitigation programs to effectively fix the price on a portion (historically ranging from 25% to 50%, depending on the jurisdiction) of its natural gas supply portfolios. The maturities of the Swaps highly correlate to forecasted purchases of natural gas, during time frames ranging from October 2011 through October 2012. Under such contracts, Southwest pays the counterparty at a fixed rate and receives from the counterparty a floating rate per MMBtu ("dekatherm") of natural gas. Only the net differential is actually paid or received. The differential is calculated based on the notional amounts under the contracts, which are detailed in the table below (thousands of dekatherms):


	September 30, 2011		December 31, 2010

Swaps contracts		11,370		14,207

Southwest does not utilize derivative financial instruments for speculative purposes, nor does it have trading operations.

Gains (losses) recognized in income for derivatives not designated as hedging instruments:

(Thousands of dollars)


		Three Months Ended						Nine Months Ended						Twelve Months Ended
Instrument	Location of Gain or (Loss) Recognized in Income on Derivative	September 30						September 30						September 30
Instrument		2011			2010			2011			2010			2011			2010

Swaps	Net cost of gas sold	$	(7,570	)	$	(12,046	)	$	(9,539	)	$	(30,013	)	$	(7,216	)	$	(33,994)
Swaps	Net cost of gas sold		7,570	^*		12,046	^*		9,539	^*		30,013	^*		7,216	^*		33,994	^*

Total		$	-		$	-		$	-		$	-		$	-		$	-

^* Represents the impact of regulatory deferral accounting treatment under U.S. GAAP for rate-regulated entities.

In January 2010, Southwest entered into two forward-starting interest rate swaps ("FSIRS") to hedge the risk of interest rate variability during the period leading up to the planned issuance of fixed-rate debt to replace $200 million of debt that matured in February 2011 and $200 million maturing in May 2012. The counterparties to each agreement are four major banking institutions. The first FSIRS was a designated cash flow hedge and terminated in December 2010 concurrent with the related issuance of $125 million 4.45% 10-year Senior Notes. The terms of the second FSIRS are as follows:


Notional amount		$100 million
Fixed rate to be paid by Southwest		4.78%
Mandatory termination date (on or before)		March 20, 2012

Southwest previously designated the second FSIRS agreement as a cash flow hedge of forecasted future interest payments. At inception of the hedge, the terms of the derivative were the same as a perfect hypothetical derivative; thus, there is an expectation that there will be no ineffectiveness, and that the effective portion of unrealized gains and losses on the FSIRS leading up to the forecasted debt issuance will be reported as a component of other comprehensive income. At termination, the final value will be reclassified from accumulated other comprehensive income into earnings over the same period the hedged forecasted transaction affects earnings. However, should conditions occur that indicate the existence of ineffectiveness (e.g., deterioration of counterparty creditworthiness, delay in the forecasted debt issuance, etc.), Southwest will measure ineffectiveness by comparing the change in fair value of the FSIRS with the change in fair value of a hypothetical swap (the hypothetical derivative method). Gains and losses due to ineffectiveness will be recognized immediately in earnings. At September 30, 2011, the remaining FSIRS continued to qualify as an effective hedge. There was no gain or loss reclassified from accumulated other comprehensive income ("AOCI") into income (effective portion) and no gain or loss recognized in income (ineffective portion) for the Company's remaining derivative designated as a hedging instrument. See Note 6 – Equity, Comprehensive Income, and Accumulated Other Comprehensive Income for additional information on both FSIRS contracts.

Gains (losses) recognized in other comprehensive income for derivatives designated as cash flow hedging instruments:


(Thousands of dollars)
	Three Months Ended						Nine Months Ended						Twelve Months Ended
	September 30, 2011			September 30, 2010			September 30, 2011			September 30, 2010			September 30, 2011			September 30, 2010
Amount of gain (loss) on unrealized FSIRS recognized in other comprehensive income on derivative (effective portion)	$	(13,237	)	$	(11,281	)	$	(16,382	)	$	(32,540	)	$	9,403		$	(32,540	)
Amount of loss on realized FSIRS recognized in other comprehensive income on derivative		-			-			-			-			(11,691	)		-

	$	(13,237	)	$	(11,281	)	$	(16,382	)	$	(32,540	)	$	(2,288	)	$	(32,540	)

The following table sets forth the fair values of the Company's Swaps and FSIRS and their location in the balance sheets (thousands of dollars):


Fair values of derivatives not designated as hedging instruments:

September 30, 2011		Asset		Liability
Instrument	Balance Sheet Location	Derivatives		Derivatives			Net Total
Swaps	Other current liabilities	$	-	$	(8,489	)	$	(8,489	)
Swaps	Other deferred credits		-		(181	)		(181	)

Total		$	-	$	(8,670	)	$	(8,670	)


December 31, 2010		Asset		Liability
Instrument	Balance Sheet Location	Derivatives		Derivatives			Net Total
Swaps	Deferred charges and other assets	$	656	$	-		$	656
Swaps	Other current liabilities		65		(11,547	)		(11,482	)

Total		$	721	$	(11,547	)	$	(10,826	)


Fair values of derivatives designated as hedging instruments:

September 30, 2011		Asset		Liability
Instrument	Balance Sheet Location	Derivatives		Derivatives			Net Total
FSIRS	Other current liabilities	$	-	$	(23,137	)	$	(23,137	)


December 31, 2010		Asset		Liability
Instrument	Balance Sheet Location	Derivatives		Derivatives			Net Total
FSIRS	Other deferred credits	$	-	$	(6,755	)	$	(6,755	)

The estimated fair values of the natural gas derivatives were determined using future natural gas index prices (as more fully described below). The Company has master netting arrangements with each counterparty that provide for the net settlement of all contracts through a single payment. As applicable, the Company has elected to reflect the net amounts in its balance sheets.

Pursuant to regulatory deferral accounting treatment for rate-regulated entities, Southwest records the unrealized gains and losses in fair value of the Swaps as a regulatory asset and/or liability. When the Swaps settle, Southwest reverses any prior positions held and records the settled position as an increase or decrease in purchased gas under the related purchased gas adjustment ("PGA") mechanism in determining its deferred PGA balances. Neither changes in fair value, nor settled amounts, of Swaps have a direct effect on earnings or other comprehensive income.

The following table shows the amounts Southwest paid to and received from counterparties for settlements of matured Swaps.


	Three Months Ended		Nine Months Ended		Twelve Months Ended
(Thousands of dollars)	September 30, 2011		September 30, 2011		September 30, 2011

Paid to counterparties	$	3,522	$	11,695	$	16,489

No amounts were received from counterparties for settlements of matured Swaps for the three months, nine months, and twelve months ended September 30, 2011.

The following table details the regulatory assets/(liabilities) offsetting the derivatives at fair value in the balance sheets (thousands of dollars).


September 30, 2011
Instrument	Balance Sheet Location	Net Total
Swaps	Prepaids and other current assets	$	8,489
Swaps	Deferred charges and other assets		181

December 31, 2010
Instrument	Balance Sheet Location	Net Total
Swaps	Other deferred credits	$	(656	)
Swaps	Prepaids and other current assets		11,482

Fair Value Measurements. The estimated fair values of Southwest's Swaps were determined at September 30, 2011 and December 31, 2010 using NYMEX futures settlement prices for delivery of natural gas at Henry Hub adjusted by the price of NYMEX ClearPort basis Swaps, which reflect the difference between the price of natural gas at a given delivery basin and the Henry Hub pricing points. These Level 2 inputs are observable in the marketplace throughout the full term of the Swaps, but have been credit-risk adjusted with no significant impact to the overall fair value measure.

The estimated fair values of Southwest's FSIRS were determined using a discounted cash flow model that utilizes forward interest rate curves. The inputs to the model are the terms of the FSIRS. These Level 2 inputs are observable in the marketplace throughout the full term of the FSIRS, but have been credit-risk adjusted with no significant impact to the overall fair value measure.

The following table sets forth, by level within the three-level fair value hierarchy that ranks the inputs used to measure fair value by their reliability, the Company's financial assets and liabilities that were accounted for at fair value:


Level 2 – Significant other observable inputs

(Thousands of dollars)	September 30, 2011			December 31, 2010

Assets at fair value:
Deferred charges and other assets – Swaps	$	-		$	656

Liabilities at fair value:
Other current liabilities – Swaps		(8,489	)		(11,482	)
Other deferred credits – Swaps		(181	)		-
Other current liabilities – FSIRS		(23,137	)		-
Other deferred credits – FSIRS		-			(6,755	)

Net Assets (Liabilities)	$	(31,807	)	$	(17,581	)

No financial assets or liabilities accounted for at fair value fell within Level 1 or Level 3 of the fair value hierarchy.

Related Tax Effects of Designated Hedging Activities Allocated to Each Component of Other Comprehensive Income


	Three Months Ended September 30,
	2011									2010

	Before- Tax Amount			Tax (Expense) or Benefit (1)			Net-of- Tax Amount			Before- Tax Amount			Tax (Expense) or Benefit (1)		Net-of- Tax Amount
(Thousands of dollars)
FSIRS:
Realized/unrealized gain (loss)	$	(13,237	)	$	5,030		$	(8,207	)	$	(11,281	)	$	4,287	$	(6,994	)
Amounts reclassified into net income		292			(111	)		181			-			-		-

Other comprehensive income (loss)	$	(12,945	)	$	4,919		$	(8,026	)	$	(11,281	)	$	4,287	$	(6,994	)


	Nine Months Ended September 30,
	2011									2010
	Before- Tax Amount			Tax (Expense) or Benefit (1)			Net-of- Tax Amount			Before- Tax Amount			Tax (Expense) or Benefit (1)		Net-of- Tax Amount
(Thousands of dollars)
FSIRS:
Realized/unrealized gain (loss)	$	(16,382	)	$	6,225		$	(10,157	)	$	(32,540	)	$	12,365	$	(20,175	)
Amounts reclassified into net income		877			(333	)		544			-			-		-

Other comprehensive income (loss)	$	(15,505	)	$	5,892		$	(9,613	)	$	(32,540	)	$	12,365	$	(20,175	)


	Twelve Months Ended September 30,
	2011									2010
	Before- Tax Amount			Tax (Expense) or Benefit (1)			Net-of- Tax Amount			Before- Tax Amount			Tax (Expense) or Benefit (1)		Net-of- Tax Amount
(Thousands of dollars)
FSIRS:
Realized/unrealized gain (loss)	$	(2,288	)	$	870		$	(1,418	)	$	(32,540	)	$	12,365	$	(20,175	)
Amounts reclassified into net income		974			(370	)		604			-			-		-

Other comprehensive income (loss)	$	(1,314	)	$	500		$	(814	)	$	(32,540	)	$	12,365	$	(20,175	)

(1)	Tax amounts are calculated using a 38% rate.

- Definition

Combined disclosure of Derivatives and Fair Value Measurements. Derivatives: Describes an entity's risk management strategies, derivatives in hedging activities and non-hedging derivative instruments, the assets, obligations, liabilities, revenues and expenses arising there from, and the amounts of and methodologies and assumptions used in determining the amounts of such items. Fair Value: represents the complete disclosure regarding the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments, assets, and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the Company is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risk is are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Long-Term Debt

9 Months Ended

Sep. 30, 2011

Long-Term Debt

Long-Term Debt

Note 5 – Long-Term Debt

Carrying amounts of the Company's long-term debt and their related estimated fair values as of September 30, 2011 and December 31, 2010 are disclosed in the following table. The fair values of the revolving credit facility and the variable-rate Industrial Development Revenue Bonds ("IDRBs") approximate carrying value. Market values for the debentures, fixed-rate IDRBs, and other indebtedness were determined based on dealer quotes using trading records for September 30, 2011 and December 31, 2010, as applicable, and other secondary sources which are customarily consulted for data of this kind.


	September 30, 2011					December 31, 2010
	Carrying Amount			Market Value		Carrying Amount			Market Value
(Thousands of dollars)
Debentures:
Notes, 8.375%, due 2011	$	-		$	-	$	200,000		$	201,560
Notes, 7.625%, due 2012		200,000			207,934		200,000			214,666
Notes, 4.45%, due 2020		125,000			127,390		125,000			125,325
Notes, 6.1%, due 2041		125,000			142,146		-			-
8% Series, due 2026		75,000			95,260		75,000			99,968
Medium-term notes, 7.59% series, due 2017		25,000			30,217		25,000			30,295
Medium-term notes, 7.78% series, due 2022		25,000			31,600		25,000			32,063
Medium-term notes, 7.92% series, due 2027		25,000			31,185		25,000			33,211
Medium-term notes, 6.76% series, due 2027		7,500			8,345		7,500			8,956
Unamortized discount		(2,191	)				(2,534	)

		605,309					679,966

Revolving credit facility and commercial paper, due 2012		20,000			20,000		-			-

Industrial development revenue bonds:
Variable-rate bonds:
Tax-exempt Series A, due 2028		50,000			50,000		50,000			50,000
2003 Series A, due 2038		50,000			50,000		50,000			50,000
2008 Series A, due 2038		50,000			50,000		50,000			50,000
2009 Series A, due 2039		50,000			50,000		50,000			50,000
Fixed-rate bonds:
6.10% 1999 Series A, due 2038		12,410			12,437		12,410			11,968
5.95% 1999 Series C, due 2038		14,320			14,357		14,320			13,594
5.55% 1999 Series D, due 2038		8,270			8,082		8,270			7,468
5.45% 2003 Series C, due 2038 (rate resets in 2013)		30,000			31,579		30,000			31,547
5.25% 2003 Series D, due 2038		20,000			19,046		20,000			17,474
5.80% 2003 Series E, due 2038 (rate resets in 2013)		15,000			15,166		15,000			15,436
5.25% 2004 Series A, due 2034		65,000			62,847		65,000			58,574
5.00% 2004 Series B, due 2033		31,200			29,465		31,200			27,295
4.85% 2005 Series A, due 2035		100,000			91,905		100,000			84,485
4.75% 2006 Series A, due 2036		24,855			22,401		24,855			20,518
Unamortized discount		(3,395	)				(3,502	)

		517,660					517,553

Other		14,990			14,977		2,242			2,473

		1,157,959					1,199,761
Less: current maturities		(221,102	)				(75,080	)

Long-term debt, less current maturities	$	936,857				$	1,124,681

Equity, Comprehensive Income, And Accumulated Other Comprehensive Income

9 Months Ended

Sep. 30, 2011

Equity, Comprehensive Income, And Accumulated Other Comprehensive Income

Equity, Comprehensive Income, And Accumulated Other Comprehensive Income

Note 6 – Equity, Comprehensive Income, and Accumulated Other Comprehensive Income

The table below provides details of activity in equity during the nine months ended September 30, 2011.


(In thousands, except per share amounts)	Southwest Gas Corporation Equity
	Common Stock				Additional Paid-in Capital		Accumulated Other Comprehensive Income (Loss)			Retained Earnings			Non- controlling Interest			Total


	Shares		Amount
DECEMBER 31, 2010		45,599	$	47,229	$	807,885	$	(30,784	)	$	343,131		$	(465	)	$	1,166,996
Common stock issuances		302		302		9,150											9,452
Net income (loss)											56,963			(343	)		56,620
Other comprehensive income (loss):
Net actuarial gain arising during period, less amortization of unamortized benefit plan cost, net of tax								960									960
FSIRS unrealized loss, net of tax								(10,157	)								(10,157	)
Amounts reclassified to net income, net of tax (Note 4)								544									544
Dividends declared
Common: $0.795 per share											(36,969	)					(36,969	)

SEPTEMBER 30, 2011		45,901	$	47,531	$	817,035	$	(39,437	)	$	363,125		$	(808	)	$	1,187,446

The tables below provide details of comprehensive income and year-to-date activity in AOCI. See Note 4 – Derivatives and Fair Value Measurements for additional information on the FSIRS, including reclassifications into net income.

Comprehensive Income

(Thousands of dollars)


	Three Months Ended September 30,						Nine Months Ended September 30,						Twelve Months Ended September 30,
	2011			2010			2011			2010			2011			2010
Net income (loss)	$	(15,747	)	$	(4,964	)	$	56,620		$	58,503		$	101,570		$	104,531
Net actuarial gain (loss) arising during period, less amortization of unamortized benefit plan cost, net of tax		320			342			960			1,025			2,777			(2,419	)
FSIRS realized and unrealized losses, net of tax		(8,207	)		(6,994	)		(10,157	)		(20,175	)		(1,418	)		(20,175	)
Amounts reclassified into net income, net of tax		181			-			544			-			604			-

Comprehensive income (loss)		(23,453	)		(11,616	)		47,967			39,353			103,533			81,937
Comprehensive loss attributable to noncontrolling interest		(106	)		(141	)		(343	)		(389	)		(378	)		(753	)

Comprehensive income (loss) attributable to Southwest Gas Corporation	$	(23,347	)	$	(11,475	)	$	48,310		$	39,742		$	103,911		$	82,690

Tax (expense) benefit associated with net actuarial gain (loss) arising during period	$	(197	)	$	(209	)	$	(589	)	$	(628	)	$	(1,702	)	$	1,484

Tax benefit associated with FSIRS realized and unrealized losses recognized in other comprehensive income	$	5,030		$	4,287		$	6,225		$	12,365		$	870		$	12,365

Tax expense associated with FSIRS reclassified out of AOCI to net income	$	(111	)	$	-		$	(333	)	$	-		$	(370	)	$	-

AOCI - Rollforward

(Thousands of dollars)


	Defined Benefit Plans									FSIRS								AOCI
	Before-Tax			Tax (Expense) Benefit			After-Tax			Before-Tax			Tax (Expense) Benefit		After-Tax			AOCI
Beginning Balance AOCI December 31, 2010	$	(31,304	)	$	11,896		$	(19,408	)	$	(18,349	)	$	6,973	$	(11,376	)	$	(30,784	)
Current period change		1,549			(589	)		960	*		(15,505	)		5,892		(9,613	)**		(8,653	)

Ending Balance AOCI September 30, 2011	$	(29,755	)	$	11,307		$	(18,448	)	$	(33,854	)	$	12,865	$	(20,989	)	$	(39,437	)

*	Net actuarial gain (loss), less amortization of unamortized benefit plan cost

**	FSIRS unrealized loss of $10,157,000 recognized in other comprehensive income less the portion of the previous FSIRS realized loss that was reclassified to net income in the current period ($544,000).

Approximately $1.5 million of realized/unrealized losses (net of tax) related to the FSIRS reported in AOCI at September 30, 2011 will be reclassified into expense within the next 12 months as interest payments on the related long-term debt occur.

Nature Of Operations And Basis Of Presentation (Tables)

9 Months Ended

Sep. 30, 2011

Nature Of Operations And Basis Of Presentation

Intercompany Transactions


	September 30, 2011		December 31, 2010

Accounts receivable for NPL services	$	13,680	$	8,111

Other Income (Deductions)


	Three Months Ended						Nine Months Ended						Twelve Months Ended
	September 30						September 30						September 30
	2011			2010			2011			2010			2011			2010

Change in COLI policies	$	(6,700	)	$	7,750		$	(1,900	)	$	5,620		$	2,250		$	7,223
Interest income		118			49			308			127			375			154
Pipe replacement costs		(1,266	)		(927	)		(3,113	)		(3,918	)		(4,218	)		(4,305	)
Miscellaneous income and (expense)		(239	)		(157	)		(2,109	)		(791	)		(2,409	)		(108	)

Total other income (deductions)	$	(8,087	)	$	6,715		$	(6,814	)	$	1,038		$	(4,002	)	$	2,964

Components Of Net Periodic Benefit Cost (Tables)

9 Months Ended

Sep. 30, 2011

Components Of Net Periodic Benefit Cost

Qualified Retirement Plan With Defined Benefits


	Qualified Retirement Plan
	Period Ended September 30,
	Three Months						Nine Months						Twelve Months
	2011			2010			2011			2010			2011			2010
(Thousands of dollars)
Service cost	$	4,431		$	4,233		$	13,293		$	12,699		$	17,526		$	16,546
Interest cost		9,319			8,904			27,957			26,711			36,860			35,343
Expected return on plan assets		(10,028	)		(9,135	)		(30,085	)		(27,404	)		(39,219	)		(36,209	)
Amortization of net loss		3,587			2,620			10,761			7,859			13,380			8,922

Net periodic benefit cost	$	7,309		$	6,622		$	21,926		$	19,865		$	28,547		$	24,602


	SERP
	Period Ended September 30,
	Three Months						Nine Months						Twelve Months
	2011			2010			2011			2010			2011			2010
(Thousands of dollars)
Service cost	$	54		$	93		$	163		$	279		$	256		$	327
Interest cost		441			511			1,324			1,533			1,836			2,050
Amortization of net loss		158			289			473			867			761			1,095

Net periodic benefit cost	$	653		$	893		$	1,960		$	2,679		$	2,853		$	3,472


	PBOP
	Period Ended September 30,
	Three Months						Nine Months						Twelve Months
	2011			2010			2011			2010			2011			2010
(Thousands of dollars)
Service cost	$	215		$	214		$	644		$	642		$	858		$	824
Interest cost		658			623			1,974			1,869			2,596			2,461
Expected return on plan assets		(595	)		(523	)		(1,785	)		(1,569	)		(2,309	)		(1,970	)
Amortization of transition obligation		217			216			650			650			867			867
Amortization of net loss		147			122			442			366			565			475

Net periodic benefit cost	$	642		$	652		$	1,925		$	1,958		$	2,577		$	2,657

Segment Information (Tables)

9 Months Ended

Sep. 30, 2011

Segment Information

List Of Revenues From External Customers, Intersegment Revenues, And Segment Net Income


	Natural Gas Operations			Construction Services		Total
Three months ended September 30, 2011
Revenues from external customers	$	195,647		$	122,696	$	318,343
Intersegment revenues		-			34,249		34,249

Total	$	195,647		$	156,945	$	352,592

Segment net income (loss)	$	(25,566	)	$	9,925	$	(15,641	)


Three months ended September 30, 2010
Revenues from external customers	$	213,893		$	76,125	$	290,018
Intersegment revenues		-			17,665		17,665

Total	$	213,893		$	93,790	$	307,683

Segment net income (loss)	$	(8,813	)	$	3,990	$	(4,823	)


Nine months ended September 30, 2011
Revenues from external customers	$	1,022,914		$	280,635	$	1,303,549
Intersegment revenues		-			65,988		65,988

Total	$	1,022,914		$	346,623	$	1,369,537

Segment net income	$	42,648		$	14,315	$	56,963


Nine months ended September 30, 2010
Revenues from external customers	$	1,133,671		$	183,875	$	1,317,546
Intersegment revenues		-			44,713		44,713

Total	$	1,133,671		$	228,588	$	1,362,259

Segment net income	$	52,403		$	6,489	$	58,892


Twelve months ended September 30, 2011
Revenues from external customers	$	1,401,150		$	353,973	$	1,755,123
Intersegment revenues		-			82,526		82,526

Total	$	1,401,150		$	436,499	$	1,837,649

Segment net income	$	81,627		$	20,321	$	101,948


Twelve months ended September 30, 2010
Revenues from external customers	$	1,561,644		$	241,575	$	1,803,219
Intersegment revenues		-			57,845		57,845

Total	$	1,561,644		$	299,420	$	1,861,064

Segment net income	$	96,074		$	9,210	$	105,284

- Definition

Tabular disclosure of the profit or loss and total assets for each reportable segment. An entity discloses certain information on each reportable segment if the amounts (a) are included in the measure of segment profit or loss reviewed by the chief operating decision maker or (b) are otherwise regularly provided to the chief operating decision maker, even if not included in that measure of segment profit or loss.

+ References + Details

Derivatives And Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2011

Derivatives And Fair Value Measurements

Notional Amounts Under Swaps Contracts


	September 30, 2011		December 31, 2010

Swaps contracts		11,370		14,207

Amount Of Gain Or (Loss) Recognized In Income On Derivative


		Three Months Ended						Nine Months Ended						Twelve Months Ended
Instrument	Location of Gain or (Loss) Recognized in Income on Derivative	September 30						September 30						September 30
Instrument		2011			2010			2011			2010			2011			2010

Swaps	Net cost of gas sold	$	(7,570	)	$	(12,046	)	$	(9,539	)	$	(30,013	)	$	(7,216	)	$	(33,994)
Swaps	Net cost of gas sold		7,570	^*		12,046	^*		9,539	^*		30,013	^*		7,216	^*		33,994	^*

Total		$	-		$	-		$	-		$	-		$	-		$	-

^* Represents the impact of regulatory deferral accounting treatment under U.S. GAAP for rate-regulated entities.

Summary Of FSIRS


Notional amount		$100 million
Fixed rate to be paid by Southwest		4.78%
Mandatory termination date (on or before)		March 20, 2012

Gains (Losses) On Derivatives In Cash Flow Hedging


(Thousands of dollars)
	Three Months Ended						Nine Months Ended						Twelve Months Ended
	September 30, 2011			September 30, 2010			September 30, 2011			September 30, 2010			September 30, 2011			September 30, 2010
Amount of gain (loss) on unrealized FSIRS recognized in other comprehensive income on derivative (effective portion)	$	(13,237	)	$	(11,281	)	$	(16,382	)	$	(32,540	)	$	9,403		$	(32,540	)
Amount of loss on realized FSIRS recognized in other comprehensive income on derivative		-			-			-			-			(11,691	)		-

	$	(13,237	)	$	(11,281	)	$	(16,382	)	$	(32,540	)	$	(2,288	)	$	(32,540	)

Fair Values Of Swaps And FSIRS In Balance Sheet Location


Fair values of derivatives not designated as hedging instruments:

September 30, 2011		Asset		Liability
Instrument	Balance Sheet Location	Derivatives		Derivatives			Net Total
Swaps	Other current liabilities	$	-	$	(8,489	)	$	(8,489	)
Swaps	Other deferred credits		-		(181	)		(181	)

Total		$	-	$	(8,670	)	$	(8,670	)


December 31, 2010		Asset		Liability
Instrument	Balance Sheet Location	Derivatives		Derivatives			Net Total
Swaps	Deferred charges and other assets	$	656	$	-		$	656
Swaps	Other current liabilities		65		(11,547	)		(11,482	)

Total		$	721	$	(11,547	)	$	(10,826	)


Fair values of derivatives designated as hedging instruments:

September 30, 2011		Asset		Liability
Instrument	Balance Sheet Location	Derivatives		Derivatives			Net Total
FSIRS	Other current liabilities	$	-	$	(23,137	)	$	(23,137	)


December 31, 2010		Asset		Liability
Instrument	Balance Sheet Location	Derivatives		Derivatives			Net Total
FSIRS	Other deferred credits	$	-	$	(6,755	)	$	(6,755	)

Paid To And Received From Counterparties For Settlements Of Matured Swaps


	Three Months Ended		Nine Months Ended		Twelve Months Ended
(Thousands of dollars)	September 30, 2011		September 30, 2011		September 30, 2011

Paid to counterparties	$	3,522	$	11,695	$	16,489

Regulatory Assets/Liabilities Offsetting The Amounts In The Balance Sheet


September 30, 2011
Instrument	Balance Sheet Location	Net Total
Swaps	Prepaids and other current assets	$	8,489
Swaps	Deferred charges and other assets		181

December 31, 2010
Instrument	Balance Sheet Location	Net Total
Swaps	Other deferred credits	$	(656	)
Swaps	Prepaids and other current assets		11,482

Significant Other Observable Inputs


Level 2 – Significant other observable inputs

(Thousands of dollars)	September 30, 2011			December 31, 2010

Assets at fair value:
Deferred charges and other assets – Swaps	$	-		$	656

Liabilities at fair value:
Other current liabilities – Swaps		(8,489	)		(11,482	)
Other deferred credits – Swaps		(181	)		-
Other current liabilities – FSIRS		(23,137	)		-
Other deferred credits – FSIRS		-			(6,755	)

Net Assets (Liabilities)	$	(31,807	)	$	(17,581	)


	Three Months Ended September 30,
	2011									2010

	Before- Tax Amount			Tax (Expense) or Benefit (1)			Net-of- Tax Amount			Before- Tax Amount			Tax (Expense) or Benefit (1)		Net-of- Tax Amount
(Thousands of dollars)
FSIRS:
Realized/unrealized gain (loss)	$	(13,237	)	$	5,030		$	(8,207	)	$	(11,281	)	$	4,287	$	(6,994	)
Amounts reclassified into net income		292			(111	)		181			-			-		-

Other comprehensive income (loss)	$	(12,945	)	$	4,919		$	(8,026	)	$	(11,281	)	$	4,287	$	(6,994	)


	Nine Months Ended September 30,
	2011									2010
	Before- Tax Amount			Tax (Expense) or Benefit (1)			Net-of- Tax Amount			Before- Tax Amount			Tax (Expense) or Benefit (1)		Net-of- Tax Amount
(Thousands of dollars)
FSIRS:
Realized/unrealized gain (loss)	$	(16,382	)	$	6,225		$	(10,157	)	$	(32,540	)	$	12,365	$	(20,175	)
Amounts reclassified into net income		877			(333	)		544			-			-		-

Other comprehensive income (loss)	$	(15,505	)	$	5,892		$	(9,613	)	$	(32,540	)	$	12,365	$	(20,175	)


	Twelve Months Ended September 30,
	2011									2010
	Before- Tax Amount			Tax (Expense) or Benefit (1)			Net-of- Tax Amount			Before- Tax Amount			Tax (Expense) or Benefit (1)		Net-of- Tax Amount
(Thousands of dollars)
FSIRS:
Realized/unrealized gain (loss)	$	(2,288	)	$	870		$	(1,418	)	$	(32,540	)	$	12,365	$	(20,175	)
Amounts reclassified into net income		974			(370	)		604			-			-		-

Other comprehensive income (loss)	$	(1,314	)	$	500		$	(814	)	$	(32,540	)	$	12,365	$	(20,175	)

(1)	Tax amounts are calculated using a 38% rate.

Long-Term Debt (Tables)

9 Months Ended

Sep. 30, 2011

Long-Term Debt

Schedule Of Estimated Fair Values Of Long-Term Debt


	September 30, 2011					December 31, 2010
	Carrying Amount			Market Value		Carrying Amount			Market Value
(Thousands of dollars)
Debentures:
Notes, 8.375%, due 2011	$	-		$	-	$	200,000		$	201,560
Notes, 7.625%, due 2012		200,000			207,934		200,000			214,666
Notes, 4.45%, due 2020		125,000			127,390		125,000			125,325
Notes, 6.1%, due 2041		125,000			142,146		-			-
8% Series, due 2026		75,000			95,260		75,000			99,968
Medium-term notes, 7.59% series, due 2017		25,000			30,217		25,000			30,295
Medium-term notes, 7.78% series, due 2022		25,000			31,600		25,000			32,063
Medium-term notes, 7.92% series, due 2027		25,000			31,185		25,000			33,211
Medium-term notes, 6.76% series, due 2027		7,500			8,345		7,500			8,956
Unamortized discount		(2,191	)				(2,534	)

		605,309					679,966

Revolving credit facility and commercial paper, due 2012		20,000			20,000		-			-

Industrial development revenue bonds:
Variable-rate bonds:
Tax-exempt Series A, due 2028		50,000			50,000		50,000			50,000
2003 Series A, due 2038		50,000			50,000		50,000			50,000
2008 Series A, due 2038		50,000			50,000		50,000			50,000
2009 Series A, due 2039		50,000			50,000		50,000			50,000
Fixed-rate bonds:
6.10% 1999 Series A, due 2038		12,410			12,437		12,410			11,968
5.95% 1999 Series C, due 2038		14,320			14,357		14,320			13,594
5.55% 1999 Series D, due 2038		8,270			8,082		8,270			7,468
5.45% 2003 Series C, due 2038 (rate resets in 2013)		30,000			31,579		30,000			31,547
5.25% 2003 Series D, due 2038		20,000			19,046		20,000			17,474
5.80% 2003 Series E, due 2038 (rate resets in 2013)		15,000			15,166		15,000			15,436
5.25% 2004 Series A, due 2034		65,000			62,847		65,000			58,574
5.00% 2004 Series B, due 2033		31,200			29,465		31,200			27,295
4.85% 2005 Series A, due 2035		100,000			91,905		100,000			84,485
4.75% 2006 Series A, due 2036		24,855			22,401		24,855			20,518
Unamortized discount		(3,395	)				(3,502	)

		517,660					517,553

Other		14,990			14,977		2,242			2,473

		1,157,959					1,199,761
Less: current maturities		(221,102	)				(75,080	)

Long-term debt, less current maturities	$	936,857				$	1,124,681

- Definition

Tabular disclosure of long-debt instruments or arrangements, including identification, terms, features, collateral requirements and other information necessary to a fair presentation. These are debt arrangements that originally required repayment more than twelve months after issuance or greater than the normal operating cycle of the entity, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 22
-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28541-108399

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21475-112644

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21506-112644

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21538-112644

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21521-112644

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=6584090&loc=d3e28878-108400

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6479336&loc=d3e64711-112823

Reference 11: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(e),(f))
-URI http://asc.fasb.org/extlink&oid=6881521&loc=d3e23780-122690

+ Details

Equity, Comprehensive Income, And Accumulated Other Comprehensive Income (Tables)

9 Months Ended

Sep. 30, 2011

Equity, Comprehensive Income, And Accumulated Other Comprehensive Income

Detailed Activities Of Equity


(In thousands, except per share amounts)	Southwest Gas Corporation Equity
	Common Stock				Additional Paid-in Capital		Accumulated Other Comprehensive Income (Loss)			Retained Earnings			Non- controlling Interest			Total


	Shares		Amount
DECEMBER 31, 2010		45,599	$	47,229	$	807,885	$	(30,784	)	$	343,131		$	(465	)	$	1,166,996
Common stock issuances		302		302		9,150											9,452
Net income (loss)											56,963			(343	)		56,620
Other comprehensive income (loss):
Net actuarial gain arising during period, less amortization of unamortized benefit plan cost, net of tax								960									960
FSIRS unrealized loss, net of tax								(10,157	)								(10,157	)
Amounts reclassified to net income, net of tax (Note 4)								544									544
Dividends declared
Common: $0.795 per share											(36,969	)					(36,969	)

SEPTEMBER 30, 2011		45,901	$	47,531	$	817,035	$	(39,437	)	$	363,125		$	(808	)	$	1,187,446

Detailed Activities Of Comprehensive Income


	Three Months Ended September 30,						Nine Months Ended September 30,						Twelve Months Ended September 30,
	2011			2010			2011			2010			2011			2010
Net income (loss)	$	(15,747	)	$	(4,964	)	$	56,620		$	58,503		$	101,570		$	104,531
Net actuarial gain (loss) arising during period, less amortization of unamortized benefit plan cost, net of tax		320			342			960			1,025			2,777			(2,419	)
FSIRS realized and unrealized losses, net of tax		(8,207	)		(6,994	)		(10,157	)		(20,175	)		(1,418	)		(20,175	)
Amounts reclassified into net income, net of tax		181			-			544			-			604			-

Comprehensive income (loss)		(23,453	)		(11,616	)		47,967			39,353			103,533			81,937
Comprehensive loss attributable to noncontrolling interest		(106	)		(141	)		(343	)		(389	)		(378	)		(753	)

Comprehensive income (loss) attributable to Southwest Gas Corporation	$	(23,347	)	$	(11,475	)	$	48,310		$	39,742		$	103,911		$	82,690

Tax (expense) benefit associated with net actuarial gain (loss) arising during period	$	(197	)	$	(209	)	$	(589	)	$	(628	)	$	(1,702	)	$	1,484

Tax benefit associated with FSIRS realized and unrealized losses recognized in other comprehensive income	$	5,030		$	4,287		$	6,225		$	12,365		$	870		$	12,365

Tax expense associated with FSIRS reclassified out of AOCI to net income	$	(111	)	$	-		$	(333	)	$	-		$	(370	)	$	-

Detailed Activities Of Accumulated Other Comprehensive Income


	Defined Benefit Plans									FSIRS								AOCI
	Before-Tax			Tax (Expense) Benefit			After-Tax			Before-Tax			Tax (Expense) Benefit		After-Tax			AOCI
Beginning Balance AOCI December 31, 2010	$	(31,304	)	$	11,896		$	(19,408	)	$	(18,349	)	$	6,973	$	(11,376	)	$	(30,784	)
Current period change		1,549			(589	)		960	*		(15,505	)		5,892		(9,613	)**		(8,653	)

Ending Balance AOCI September 30, 2011	$	(29,755	)	$	11,307		$	(18,448	)	$	(33,854	)	$	12,865	$	(20,989	)	$	(39,437	)

*	Net actuarial gain (loss), less amortization of unamortized benefit plan cost

**	FSIRS unrealized loss of $10,157,000 recognized in other comprehensive income less the portion of the previous FSIRS realized loss that was reclassified to net income in the current period ($544,000).

Nature Of Operations And Basis Of Presentation (Intercompany Transactions) (Details) - USD ($) $ in Thousands	1 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2011	Sep. 30, 2011	Dec. 31, 2010
Accounts receivable for NPL services	$ 119,576	$ 119,576	$ 147,605
Goodwill and other intangibles test of impairment more likelihood percentage	50.00%
Decrease in revenues and regulatory assets		(3,700)	(2,900)
NPL Construction Co [Member]
Accounts receivable for NPL services	$ 13,680	$ 13,680	$ 8,111

Nature Of Operations And Basis Of Presentation (Other Income (Deductions)) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Nature Of Operations And Basis Of Presentation
Change in COLI policies	$ (6,700)	$ 7,750	$ (1,900)	$ 5,620	$ 2,250	$ 7,223
Interest income	118	49	308	127	375	154
Pipe replacement costs	(1,266)	(927)	(3,113)	(3,918)	(4,218)	(4,305)
Miscellaneous income and (expense)	(239)	(157)	(2,109)	(791)	(2,409)	(108)
Total other income (deductions)	$ (8,087)	$ 6,715	$ (6,814)	$ 1,038	$ (4,002)	$ 2,964

Components Of Net Periodic Benefit Cost (Qualified Retirement Plan With Defined Benefits) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Qualified Retirement Plan [Member]
Service cost	$ 4,431	$ 4,233	$ 13,293	$ 12,699	$ 17,526	$ 16,546
Interest cost	9,319	8,904	27,957	26,711	36,860	35,343
Expected return on plan assets	(10,028)	(9,135)	(30,085)	(27,404)	(39,219)	(36,209)
Amortization of net loss	3,587	2,620	10,761	7,859	13,380	8,922
Net periodic benefit cost	7,309	6,622	21,926	19,865	28,547	24,602
SERP [Member]
Service cost	54	93	163	279	256	327
Interest cost	441	511	1,324	1,533	1,836	2,050
Amortization of net loss	158	289	473	867	761	1,095
Net periodic benefit cost	653	893	1,960	2,679	2,853	3,472
PBOP [Member]
Service cost	215	214	644	642	858	824
Interest cost	658	623	1,974	1,869	2,596	2,461
Expected return on plan assets	(595)	(523)	(1,785)	(1,569)	(2,309)	(1,970)
Amortization of transition obligation	217	216	650	650	867	867
Amortization of net loss	147	122	442	366	565	475
Net periodic benefit cost	$ 642	$ 652	$ 1,925	$ 1,958	$ 2,577	$ 2,657

- Definition

An amount calculated as a basis for determining the extent of delayed recognition of the effects of changes in the fair value of assets. The expected return on plan assets is determined based on the expected long-term rate of return on plan assets and the market-related value of plan assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 132R
-Paragraph 5
-Subparagraph h
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 106
-Paragraph 518
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 87
-Paragraph 264
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (h)(3)
-URI http://asc.fasb.org/extlink&oid=6962843&loc=d3e1928-114920

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Expected Return on Plan Assets
-URI http://asc.fasb.org/extlink&oid=6512136
-Topic 715
-SubTopic 30

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Expected Return on Plan Assets
-URI http://asc.fasb.org/extlink&oid=6512171
-Topic 715
-SubTopic 60

+ Details

- Definition

The increase in a defined benefit pension plan's projected benefit obligation or a defined benefit postretirement plan's accumulated postretirement benefit obligation due to the passage of time.

+ References + Details

- Definition

The actuarial present value of benefits attributed by the pension benefit formula to services rendered by employees during the period. The portion of the expected postretirement benefit obligation attributed to employee service during the period. The service cost component is a portion of the benefit obligation and is unaffected by the funded status of the plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 106
-Paragraph 518
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 87
-Paragraph 264
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 132R
-Paragraph 5
-Subparagraph a, h
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (h)(1)
-URI http://asc.fasb.org/extlink&oid=6962843&loc=d3e1928-114920

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=6962843&loc=d3e1928-114920

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Service Cost (Component of Net Periodic Pension Cost)
-URI http://asc.fasb.org/extlink&oid=6525008

+ Details

Segment Information (List Of Revenues From External Customers, Intersegment Revenues, And Segment Net Income) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Revenues from external customers	$ 318,343	$ 290,018	$ 1,303,549	$ 1,317,546	$ 1,755,123	$ 1,803,219
Intersegment revenues	34,249	17,665	65,988	44,713	82,526	57,845
Total operating revenues	352,592	307,683	1,369,537	1,362,259	1,837,649	1,861,064
Segment net income (loss)	(15,641)	(4,823)	56,963	58,892	101,948	105,284
Natural Gas Operations [Member]
Revenues from external customers	195,647	213,893	1,022,914	1,133,671	1,401,150	1,561,644
Intersegment revenues
Total operating revenues	195,647	213,893	1,022,914	1,133,671	1,401,150	1,561,644
Segment net income (loss)	(25,566)	(8,813)	42,648	52,403	81,627	96,074
Construction Services [Member]
Revenues from external customers	122,696	76,125	280,635	183,875	353,973	241,575
Intersegment revenues	34,249	17,665	65,988	44,713	82,526	57,845
Total operating revenues	156,945	93,790	346,623	228,588	436,499	299,420
Segment net income (loss)	$ 9,925	$ 3,990	$ 14,315	$ 6,489	$ 20,321	$ 9,210

Derivatives And Fair Value Measurements (Narrative) (Details) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2011 USD ($)	Sep. 30, 2010 USD ($)	Sep. 30, 2011 USD ($)	Sep. 30, 2010 USD ($)
Natural gas portfolios, minimum % rate	25.00%
Natural gas portfolios, maximum % rate	50.00%
Maturities of natural gas swaps, minimum	October 2011		October 2011
Maturities of natural gas swaps, maximum	October 2012		October 2012
Retirement of long-term debt	$ 275,065	$ 3,301	$ 275,091	$ 3,632
May 2012 [Member]
Debt maturing date	May 2012
Retirement of long-term debt	$ 200,000
February 2011 [Member]
Debt maturing date	February 2011
Retirement of long-term debt	$ 200,000
Notes, 4.45%, Due 2020 [Member]
Notes payable	$ 125,000		$ 125,000
Debt instrument interest rate	4.45%		4.45%
Issuance of fixed rate debt (in years)	10

Derivatives And Fair Value Measurements (Notional Amounts Under Swaps Contracts) (Details) - Mmbtu Mmbtu in Thousands	Sep. 30, 2011	Dec. 31, 2010
Derivatives And Fair Value Measurements
Swaps contracts	11,370	14,207

Derivatives And Fair Value Measurements (Amount Of Gain Or (Loss) Recognized In Income On Derivative) (Details) - Swaps Contracts [Member] - Net Cost Of Gas Sold [Member] - USD ($)
$ in Thousands

3 Months Ended

9 Months Ended

12 Months Ended

Sep. 30, 2011

Sep. 30, 2010

Sep. 30, 2011

Sep. 30, 2010

Sep. 30, 2011

Sep. 30, 2010

Amount of (loss) recognized in income on derivative

$ (7,570)

$ (12,046)

$ (9,539)

$ (30,013)

$ (7,216)

$ (33,994)

Amount of gain or (loss) recognized in income on derivative

^[1]

$ 7,570

12,046

$ 9,539

30,013

$ 7,216

33,994

Amount of gain or (loss) recognized in income on derivative, total

[1]	Represents the impact of regulatory deferral accounting treatment under U.S. GAAP for rate-regulated entities.

- Definition

The amount of net gains and losses recognized in income during the period on derivative instruments designated and qualifying as hedging instruments in fair value hedges and related hedged items designated and qualifying in fair value hedges, on derivative instruments designated and qualifying as hedging instruments in cash flow hedges, and on derivative instruments not designated as hedging instruments.

+ References + Details

- Definition

The amount of gain recognized in income during the period on derivative instruments designated and qualifying as hedging instruments in fair value hedges and related hedged items designated and qualifying in fair value hedges, on derivative instruments designated and qualifying as hedging instruments in cash flow hedges, and on derivative instruments not designated as hedging instruments.

+ References + Details

- Definition

The amount of loss recognized in income during the period on derivative instruments designated and qualifying as hedging instruments in fair value hedges and related hedged items designated and qualifying in fair value hedges, on derivative instruments designated and qualifying as hedging instruments in cash flow hedges, and on derivative instruments not designated as hedging instruments.

+ References + Details

Derivatives And Fair Value Measurements (Summary Of FSIRS) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2011 USD ($)
Derivatives And Fair Value Measurements
Notional amount	$ 100
Fixed rate to be paid by Southwest	4.78%
Mandatory termination date (on or before)	Mar. 20, 2012

Derivatives And Fair Value Measurements (Gains (Losses) On Derivatives In Cash Flow Hedging) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Derivatives And Fair Value Measurements
Amount of gain (loss) on unrealized FSIRS recognized in other comprehensive income on derivative (effective portion)	$ (13,237)	$ (11,281)	$ (16,382)	$ (32,540)	$ 9,403	$ (32,540)
Amount of loss on realized FSIRS recognized in other comprehensive income on derivative					(11,691)
Amount of gain (loss) on realized FSIRS recognized in other comprehensive income on derivative	$ (13,237)	$ (11,281)	$ (16,382)	$ (32,540)	$ (2,288)	$ (32,540)

Derivatives And Fair Value Measurements (Fair Values Of Swaps And FSIRS In Balance Sheet Location) (Details) - USD ($) $ in Thousands	Sep. 30, 2011	Dec. 31, 2010
FSIRS [Member] \| Other Current Liabilities [Member]
Assets derivatives designated as hedging instruments
Liability derivatives designated as hedging instruments	(23,137)
Net total designated as hedging instruments	(23,137)
FSIRS [Member] \| Other Deferred Credits [Member]
Assets derivatives designated as hedging instruments
Liability derivatives designated as hedging instruments		(6,755)
Net total designated as hedging instruments		(6,755)
Swaps [Member]
Asset derivatives not designated as hedging instruments		721
Liability derivatives not designated as hedging instruments	(8,670)	(11,547)
Net total not designated as hedging instruments	(8,670)	(10,826)
Swaps [Member] \| Deferred Charges And Other Assets [Member]
Asset derivatives not designated as hedging instruments		656
Liability derivatives not designated as hedging instruments
Net total not designated as hedging instruments		656
Swaps [Member] \| Other Current Liabilities [Member]
Asset derivatives not designated as hedging instruments		65
Liability derivatives not designated as hedging instruments	(8,489)	(11,547)
Net total not designated as hedging instruments	(8,489)	$ (11,482)
Swaps [Member] \| Other Deferred Credits [Member]
Asset derivatives not designated as hedging instruments
Liability derivatives not designated as hedging instruments	(181)
Net total not designated as hedging instruments	$ (181)

Derivatives And Fair Value Measurements (Paid To And Received From Counterparties For Settlements Of Matured Swaps) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2011	Sep. 30, 2011	Sep. 30, 2011
Derivatives And Fair Value Measurements
Paid to counterparties	$ 3,522	$ 11,695	$ 16,489

Derivatives And Fair Value Measurements (Regulatory Assets/Liabilities Offsetting the Amounts In The Balance Sheet) (Details) - Swaps [Member] - USD ($) $ in Thousands	Sep. 30, 2011	Dec. 31, 2010
Deferred Charges And Other Assets [Member]
Net Total	$ 181
Prepaids And Other Current Assets [Member]
Net Total	$ 8,489	$ 11,482
Other Deferred Credits [Member]
Net Total		$ (656)

Derivatives And Fair Value Measurements (Significant Other Observable Inputs) (Details) - Level 2 - Significant Other Observable Inputs [Member] - USD ($) $ in Thousands	Sep. 30, 2011	Dec. 31, 2010
Net Assets (Liabilities)	$ (31,807)	$ (17,581)
FSIRS [Member] \| Other Current Liabilities [Member]
Derivative Liabilities	(23,137)
FSIRS [Member] \| Other Deferred Credits [Member]
Derivative Liabilities		(6,755)
Swaps [Member] \| Deferred Charges And Other Assets [Member]
Derivative Assets		656
Swaps [Member] \| Other Current Liabilities [Member]
Derivative Liabilities	(8,489)	$ (11,482)
Swaps [Member] \| Other Deferred Credits [Member]
Derivative Liabilities	$ (181)

- Definition

Fair values as of the balance sheet date of all assets resulting from contracts that meet the criteria of being accounted for as derivative instruments, net of the effects of master netting arrangements.

+ References + Details

- Definition

Fair values as of the balance sheet date of all liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments, net of the effects of master netting arrangements.

+ References + Details

Derivatives And Fair Value Measurements (Related Tax Effects Of Designated Hedging Activities Allocated To Each Component Of Other Comprehensive Income) (Details) - USD ($)
$ in Thousands

3 Months Ended

9 Months Ended

12 Months Ended

Sep. 30, 2011

Sep. 30, 2010

Sep. 30, 2011

Sep. 30, 2010

Sep. 30, 2011

Sep. 30, 2010

Derivatives And Fair Value Measurements

Realized/unrealized gain (loss), Before Tax

$ (13,237)

$ (11,281)

$ (16,382)

$ (32,540)

$ (2,288)

$ (32,540)

Amounts reclassified into net income, Before Tax

292

877

974

Other comprehensive (income) loss, Before Tax

(12,945)

(11,281)

(15,505)

(32,540)

(1,314)

(32,540)

Realized/unrealized gain (loss), Tax

^[1]

5,030

4,287

6,225

12,365

870

12,365

Amounts reclassified into net income, Tax

^[1]

(111)

(333)

(370)

Other comprehensive (income) loss, Tax

^[1]

4,919

4,287

5,892

12,365

500

12,365

Realized/unrealized gain (loss), Net of Tax

(8,207)

(6,994)

(10,157)

(20,175)

(1,418)

(20,175)

Amounts reclassified to net income, net of tax

181

544

604

Other Comprehensive Income (Loss), Net of Tax

$ (8,026)

$ (6,994)

$ (9,613)

^[2]

$ (20,175)

$ (814)

$ (20,175)

Calculated Tax Rate

38.00%

[1]	Tax amounts are calculated using a 38% rate.
[2]	FSIRS unrealized loss of $10,157,000 recognized in other comprehensive income less the portion of the previous FSIRS realized loss that was reclassified to net income in the current period ($544,000).

Long-Term Debt (Schedule Of Estimated Fair Values Of Long-Term Debt) (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2011 USD ($)	Dec. 31, 2010 USD ($)
Less: current maturities	$ (221,102)	$ (75,080)
Long-term debt, less current maturities	936,857	1,124,681
Carrying Amount [Member]
Unamortized discount	(3,395)	(3,502)
Long-term debt, gross	1,157,959	1,199,761
Less: current maturities	(221,102)	(75,080)
Long-term debt, less current maturities	$ 936,857	1,124,681
Notes, 8.375%, Due 2011 [Member]
Debt instrument interest rate	8.375%
Debt instrument due date	2,011
Notes, 8.375%, Due 2011 [Member] \| Carrying Amount [Member]
Notes payable		200,000
Notes, 8.375%, Due 2011 [Member] \| Market Value [Member]
Notes payable, fair value disclosure		201,560
Notes, 7.625%, Due 2012 [Member]
Debt instrument interest rate	7.625%
Debt instrument due date	2,012
Notes, 7.625%, Due 2012 [Member] \| Carrying Amount [Member]
Notes payable	$ 200,000	200,000
Notes, 7.625%, Due 2012 [Member] \| Market Value [Member]
Notes payable, fair value disclosure	207,934	214,666
Notes, 4.45%, Due 2020 [Member]
Notes payable	$ 125,000
Debt instrument interest rate	4.45%
Debt instrument due date	2,020
Notes, 4.45%, Due 2020 [Member] \| Carrying Amount [Member]
Notes payable	$ 125,000	125,000
Notes, 4.45%, Due 2020 [Member] \| Market Value [Member]
Notes payable, fair value disclosure	$ 127,390	125,325
Notes, 6.1%, Due 2041 [Member]
Debt instrument interest rate	6.10%
Debt instrument due date	2,041
Notes, 6.1%, Due 2041 [Member] \| Carrying Amount [Member]
Notes payable	$ 125,000
Notes, 6.1%, Due 2041 [Member] \| Market Value [Member]
Notes payable, fair value disclosure	$ 142,146
8% Series, Due 2026 [Member]
Debt instrument interest rate	8.00%
Debt instrument due date	2,026
8% Series, Due 2026 [Member] \| Carrying Amount [Member]
Notes payable	$ 75,000	75,000
8% Series, Due 2026 [Member] \| Market Value [Member]
Notes payable, fair value disclosure	$ 95,260	99,968
Medium-Term Notes, 7.59% Series, Due 2017 [Member]
Debt instrument interest rate	7.59%
Debt instrument due date	2,017
Medium-Term Notes, 7.59% Series, Due 2017 [Member] \| Carrying Amount [Member]
Notes payable	$ 25,000	25,000
Medium-Term Notes, 7.59% Series, Due 2017 [Member] \| Market Value [Member]
Notes payable, fair value disclosure	$ 30,217	30,295
Medium-Term Notes, 7.78% Series, Due 2022 [Member]
Debt instrument interest rate	7.78%
Debt instrument due date	2,022
Medium-Term Notes, 7.78% Series, Due 2022 [Member] \| Carrying Amount [Member]
Notes payable	$ 25,000	25,000
Medium-Term Notes, 7.78% Series, Due 2022 [Member] \| Market Value [Member]
Notes payable, fair value disclosure	$ 31,600	32,063
Medium-Term Notes, 7.92% Series, Due 2027 [Member]
Debt instrument interest rate	7.92%
Debt instrument due date	2,027
Medium-Term Notes, 7.92% Series, Due 2027 [Member] \| Carrying Amount [Member]
Notes payable	$ 25,000	25,000
Medium-Term Notes, 7.92% Series, Due 2027 [Member] \| Market Value [Member]
Notes payable, fair value disclosure	$ 31,185	33,211
Medium-Term Notes, 6.76% Series, Due 2027 [Member]
Debt instrument interest rate	6.76%
Debt instrument due date	2,027
Medium-Term Notes, 6.76% Series, Due 2027 [Member] \| Carrying Amount [Member]
Notes payable	$ 7,500	7,500
Medium-Term Notes, 6.76% Series, Due 2027 [Member] \| Market Value [Member]
Notes payable, fair value disclosure	8,345	8,956
Notes Payable [Member] \| Carrying Amount [Member]
Notes payable	$ 605,309	679,966
Revolving Credit Facility And Commercial Paper, Due 2012 [Member]
Debt instrument due date	2,012
Revolving Credit Facility And Commercial Paper, Due 2012 [Member] \| Carrying Amount [Member]
Line of credit facility	$ 20,000
Revolving Credit Facility And Commercial Paper, Due 2012 [Member] \| Market Value [Member]
Line of credit facility, fair value	$ 20,000
Tax-Exempt Series A, Due 2028 [Member]
Debt instrument due date	2,028
2003 Series A, Due 2038 [Member]
Debt instrument due date	2,038
2008 Series A, Due 2038 [Member]
Debt instrument due date	2,038
2009 Series A, Due 2039 [Member]
Debt instrument due date	2,039
6.10% 1999 Series A, Due 2038 [Member]
Debt instrument interest rate	6.10%
Debt instrument due date	2,038
5.95% 1999 Series C, Due 2038 [Member]
Debt instrument interest rate	5.95%
Debt instrument due date	2,038
5.55% 1999 Series D, Due 2038 [Member]
Debt instrument interest rate	5.55%
Debt instrument due date	2,038
5.45% 2003 Series C, Due 2038 (Rate Resets In 2013) [Member]
Debt instrument interest rate	5.45%
Debt instrument due date	2,038
Debt instrument rate reset	2,013
5.25% 2003 Series D, Due 2038 [Member]
Debt instrument interest rate	5.25%
Debt instrument due date	2,038
5.80% 2003 Series E, Due 2038 (Rate Resets In 2013) [Member]
Debt instrument interest rate	5.80%
Debt instrument due date	2,038
Debt instrument rate reset	2,013
5.25% 2004 Series A, Due 2034 [Member]
Debt instrument interest rate	5.25%
Debt instrument due date	2,034
5.00% 2004 Series B, Due 2033 [Member]
Debt instrument interest rate	5.00%
Debt instrument due date	2,033
4.85% 2005 Series A, Due 2035 [Member]
Debt instrument interest rate	4.85%
Debt instrument due date	2,035
4.75% 2006 Series A, Due 2036 [Member]
Debt instrument interest rate	4.75%
Debt instrument due date	2,036
Bonds [Member] \| Carrying Amount [Member]
Unsecured debt	$ 517,660	517,553
Other Long-Term Debt [Member] \| Carrying Amount [Member]
Other	14,990	2,242
Other Long-Term Debt [Member] \| Market Value [Member]
Other long-term debt fair value	14,977	2,473
Debentures [Member] \| Carrying Amount [Member]
Unamortized discount	(2,191)	(2,534)
Variable-Rate Bonds [Member] \| Tax-Exempt Series A, Due 2028 [Member] \| Carrying Amount [Member]
Unsecured debt	50,000	50,000
Variable-Rate Bonds [Member] \| Tax-Exempt Series A, Due 2028 [Member] \| Market Value [Member]
Unsecured Debt Fair Value	50,000	50,000
Variable-Rate Bonds [Member] \| 2003 Series A, Due 2038 [Member] \| Carrying Amount [Member]
Unsecured debt	50,000	50,000
Variable-Rate Bonds [Member] \| 2003 Series A, Due 2038 [Member] \| Market Value [Member]
Unsecured Debt Fair Value	50,000	50,000
Variable-Rate Bonds [Member] \| 2008 Series A, Due 2038 [Member] \| Carrying Amount [Member]
Unsecured debt	50,000	50,000
Variable-Rate Bonds [Member] \| 2008 Series A, Due 2038 [Member] \| Market Value [Member]
Unsecured Debt Fair Value	50,000	50,000
Variable-Rate Bonds [Member] \| 2009 Series A, Due 2039 [Member] \| Carrying Amount [Member]
Unsecured debt	50,000	50,000
Variable-Rate Bonds [Member] \| 2009 Series A, Due 2039 [Member] \| Market Value [Member]
Unsecured Debt Fair Value	50,000	50,000
Fixed-Rate Bonds [Member] \| 6.10% 1999 Series A, Due 2038 [Member] \| Carrying Amount [Member]
Unsecured debt	12,410	12,410
Fixed-Rate Bonds [Member] \| 6.10% 1999 Series A, Due 2038 [Member] \| Market Value [Member]
Unsecured Debt Fair Value	12,437	11,968
Fixed-Rate Bonds [Member] \| 5.95% 1999 Series C, Due 2038 [Member] \| Carrying Amount [Member]
Unsecured debt	14,320	14,320
Fixed-Rate Bonds [Member] \| 5.95% 1999 Series C, Due 2038 [Member] \| Market Value [Member]
Unsecured Debt Fair Value	14,357	13,594
Fixed-Rate Bonds [Member] \| 5.55% 1999 Series D, Due 2038 [Member] \| Carrying Amount [Member]
Unsecured debt	8,270	8,270
Fixed-Rate Bonds [Member] \| 5.55% 1999 Series D, Due 2038 [Member] \| Market Value [Member]
Unsecured Debt Fair Value	8,082	7,468
Fixed-Rate Bonds [Member] \| 5.45% 2003 Series C, Due 2038 (Rate Resets In 2013) [Member] \| Carrying Amount [Member]
Unsecured debt	30,000	30,000
Fixed-Rate Bonds [Member] \| 5.45% 2003 Series C, Due 2038 (Rate Resets In 2013) [Member] \| Market Value [Member]
Unsecured Debt Fair Value	31,579	31,547
Fixed-Rate Bonds [Member] \| 5.25% 2003 Series D, Due 2038 [Member] \| Carrying Amount [Member]
Unsecured debt	20,000	20,000
Fixed-Rate Bonds [Member] \| 5.25% 2003 Series D, Due 2038 [Member] \| Market Value [Member]
Unsecured Debt Fair Value	19,046	17,474
Fixed-Rate Bonds [Member] \| 5.80% 2003 Series E, Due 2038 (Rate Resets In 2013) [Member] \| Carrying Amount [Member]
Unsecured debt	15,000	15,000
Fixed-Rate Bonds [Member] \| 5.80% 2003 Series E, Due 2038 (Rate Resets In 2013) [Member] \| Market Value [Member]
Unsecured Debt Fair Value	15,166	15,436
Fixed-Rate Bonds [Member] \| 5.25% 2004 Series A, Due 2034 [Member] \| Carrying Amount [Member]
Unsecured debt	65,000	65,000
Fixed-Rate Bonds [Member] \| 5.25% 2004 Series A, Due 2034 [Member] \| Market Value [Member]
Unsecured Debt Fair Value	62,847	58,574
Fixed-Rate Bonds [Member] \| 5.00% 2004 Series B, Due 2033 [Member] \| Carrying Amount [Member]
Unsecured debt	31,200	31,200
Fixed-Rate Bonds [Member] \| 5.00% 2004 Series B, Due 2033 [Member] \| Market Value [Member]
Unsecured Debt Fair Value	29,465	27,295
Fixed-Rate Bonds [Member] \| 4.85% 2005 Series A, Due 2035 [Member] \| Carrying Amount [Member]
Unsecured debt	100,000	100,000
Fixed-Rate Bonds [Member] \| 4.85% 2005 Series A, Due 2035 [Member] \| Market Value [Member]
Unsecured Debt Fair Value	91,905	84,485
Fixed-Rate Bonds [Member] \| 4.75% 2006 Series A, Due 2036 [Member] \| Carrying Amount [Member]
Unsecured debt	24,855	24,855
Fixed-Rate Bonds [Member] \| 4.75% 2006 Series A, Due 2036 [Member] \| Market Value [Member]
Unsecured Debt Fair Value	$ 22,401	$ 20,518

Equity, Comprehensive Income, And Accumulated Other Comprehensive Income (Detailed Activities Of Equity) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
DECEMBER 31, 2010, Shares			45,599,036
DECEMBER 31, 2010, Values			$ 1,166,996
Common stock issuances, Values			9,452
Net income (loss)	$ (15,747)	$ (4,964)	56,620	$ 58,503	$ 101,570	$ 104,531
Net actuarial gain arising during period, less amortization of unamortized benefit plan cost, net of tax			960
FSIRS unrealized loss, net of tax			(10,157)
Amounts reclassified to net income, net of tax	$ 181		544		$ 604
Dividends declared Common: $0.795 per share			$ (36,969)
SEPTEMBER 30, 2011, Shares	45,901,110		45,901,110		45,901,110
SEPTEMBER 30, 2011, Values	$ 1,187,446		$ 1,187,446		$ 1,187,446
Dividends declared per share	$ 0.2650	$ 0.2500	$ 0.7950	$ 0.7500	$ 1.0450	$ 0.9875
Common Stock [Member]
DECEMBER 31, 2010, Shares			45,599,000
DECEMBER 31, 2010, Values			$ 47,229
Common stock issuances, Shares			302,000
Common stock issuances, Values			$ 302
SEPTEMBER 30, 2011, Shares	45,901,000		45,901,000		45,901,000
SEPTEMBER 30, 2011, Values	$ 47,531		$ 47,531		$ 47,531
Additional Paid-In Capital [Member]
DECEMBER 31, 2010, Values			807,885
Common stock issuances, Values			9,150
SEPTEMBER 30, 2011, Values	817,035		817,035		817,035
Accumulated Other Comprehensive Income (Loss) [Member]
DECEMBER 31, 2010, Values			(30,784)
Net actuarial gain arising during period, less amortization of unamortized benefit plan cost, net of tax			960
FSIRS unrealized loss, net of tax			(10,157)
Amounts reclassified to net income, net of tax			544
SEPTEMBER 30, 2011, Values	(39,437)		(39,437)		(39,437)
Retained Earnings [Member]
DECEMBER 31, 2010, Values			343,131
Net income (loss)			56,963
Dividends declared Common: $0.795 per share			(36,969)
SEPTEMBER 30, 2011, Values	363,125		363,125		363,125
Non-Controlling Interest [Member]
DECEMBER 31, 2010, Values			(465)
Net income (loss)			(343)
SEPTEMBER 30, 2011, Values	$ (808)		$ (808)		$ (808)

Equity, Comprehensive Income, And Accumulated Other Comprehensive Income (Detailed Activities Of Comprehensive Income) (Details) - USD ($)
$ in Thousands

3 Months Ended

9 Months Ended

12 Months Ended

Sep. 30, 2011

Sep. 30, 2010

Sep. 30, 2011

Sep. 30, 2010

Sep. 30, 2011

Sep. 30, 2010

Equity, Comprehensive Income, And Accumulated Other Comprehensive Income

Net income (loss)

$ (15,747)

$ (4,964)

$ 56,620

$ 58,503

$ 101,570

$ 104,531

Net actuarial gain (loss) arising during period, less amortization of unamortized benefit plan cost, net of tax

320

342

960

^[1]

1,025

2,777

(2,419)

FSIRS realized and unrealized losses, net of tax

(8,207)

(6,994)

(10,157)

(20,175)

(1,418)

(20,175)

Amounts reclassified to net income, net of tax

181

544

604

Comprehensive income (loss)

(23,453)

(11,616)

47,967

39,353

103,533

81,937

Comprehensive loss attributable to noncontrolling interest

(106)

(141)

(343)

(389)

(378)

(753)

Comprehensive income (loss) attributable to Southwest Gas Corporation

(23,347)

(11,475)

48,310

39,742

103,911

82,690

Tax (expense) benefit associated with net actuarial gain (loss) arising during period

(197)

(209)

(589)

(628)

(1,702)

1,484

Tax benefit associated with FSIRS realized and unrealized losses recognized in other comprehensive income

5,030

$ 4,287

6,225

$ 12,365

870

$ 12,365

Tax expense associated with FSIRS reclassified out of AOCI to net income

^[2]

$ (111)

$ (333)

$ (370)

[1]	Net actuarial gain (loss), less amortization of unamortized benefit plan cost
[2]	Tax amounts are calculated using a 38% rate.

Equity, Comprehensive Income, And Accumulated Other Comprehensive Income (Detailed Activities Of Accumulated Other Comprehensive Income) (Details) - USD ($)
$ in Thousands

3 Months Ended

9 Months Ended

12 Months Ended

Sep. 30, 2011

Sep. 30, 2010

Sep. 30, 2011

Sep. 30, 2010

Sep. 30, 2011

Sep. 30, 2010

Equity, Comprehensive Income, And Accumulated Other Comprehensive Income

Beginning Balance AOCI December 31, 2010, Defined Benefit Plans - Before Tax

$ (31,304)

Beginning Balance AOCI December 31, 2010, Defined Benefit Plans - Tax (Expense) Benefit

11,896

Beginning Balance AOCI December 31, Defined Benefit Plans - After-Tax

(19,408)

Beginning Balance AOCI December 31, 2010, FSIRS - Before-Tax

(18,349)

Beginning Balance AOCI December 31, 2010, FSIRS - Tax (Expense) Benefit

6,973

Beginning Balance AOCI December 31, 2010, FSIRS - After-Tax

(11,376)

Current period change, Defined Benefit Plans - Before-Tax

1,549

Current period change, Defined Benefit Plans - Tax (Expense) Benefit

$ (197)

$ (209)

(589)

$ (628)

$ (1,702)

$ 1,484

Current period change, Defined Benefit Plans - After-Tax

320

342

960

^[1]

1,025

2,777

(2,419)

Current period change, FSIRS - Before-Tax

(15,505)

Current period change, FSIRS - Tax (Expense) Benefit

5,892

Current period change, FSIRS - After-Tax

(8,026)

$ (6,994)

(9,613)

^[2]

$ (20,175)

(814)

$ (20,175)

Beginning balance AOCI December 31,2010

(30,784)

AOCI, current period change

(8,653)

Ending Balance AOCI September 30, 2011, Defined Benefit Plans - Before Tax

(29,755)

Ending Balance AOCI September 30, 2011, Defined Benefit Plans - Tax (Expense) Benefit

11,307

Ending Balance AOCI September 30, 2011, Defined Benefit Plans - After Tax

(18,448)

(19,408)

(18,448)

Ending Balance AOCI September 30, 2011, FSIRS - Before-Tax

(33,854)

Ending Balance AOCI September 30, 2011, FSIRS - Tax (Expense) Benefit

12,865

Ending Balance AOCI September 30, 2011, FSIRS - After-Tax

(20,989)

Ending Balance AOCI September 30, 2011

(39,437)

FSIRS realized and unrealized gains (losses), Net of Tax

(10,157)

Amounts reclassified to net income, net of tax (Note 4)

(181)

$ (544)

(604)

Amount of FSIRS existing AOCI losses expected to reclassified income in next 12 months

$ 1,500

[1]	Net actuarial gain (loss), less amortization of unamortized benefit plan cost
[2]	FSIRS unrealized loss of $10,157,000 recognized in other comprehensive income less the portion of the previous FSIRS realized loss that was reclassified to net income in the current period ($544,000).