Southwest Gas 10-Q 5 Nov 15 2015 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2015	Oct. 28, 2015
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2015
Document Fiscal Year Focus	2,015
Document Fiscal Period Focus	Q3
Trading Symbol	SWX
Entity Registrant Name	SOUTHWEST GAS CORP
Entity Central Index Key	92,416
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		47,375,398

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Utility plant:
Gas plant	$ 5,734,807	$ 5,556,599
Less: accumulated depreciation	(2,060,402)	(1,973,098)
Acquisition adjustments, net	415	550
Construction work in progress	118,554	74,332
Net utility plant	3,793,374	3,658,383
Other property and investments	319,243	326,743
Restricted cash	0	821
Current assets:
Cash and cash equivalents	32,959	39,566
Accounts receivable, net of allowances	269,058	281,824
Accrued utility revenue	32,200	73,900
Income taxes receivable, net	37,810	21,853
Deferred income taxes, net	291	2,109
Deferred purchased gas costs	815	87,556
Prepaids and other current assets	105,438	99,975
Total current assets	478,571	606,783
Noncurrent assets:
Goodwill	129,884	143,160
Deferred income taxes	1,688	0
Deferred charges and other assets	460,906	478,625
Total noncurrent assets	592,478	621,785
Total assets	5,183,666	5,214,515
Capitalization:
Common stock, $1 par (authorized-60,000,000 shares; issued and outstanding-47,375,398 and 46,523,184 shares)	49,005	48,153
Additional paid-in capital	894,625	851,381
Accumulated other comprehensive income (loss), net	(48,013)	(50,175)
Retained earnings	654,492	639,164
Total Southwest Gas Corporation equity	1,550,109	1,488,523
Noncontrolling interest	(2,177)	(2,257)
Total equity	1,547,932	1,486,266
Redeemable noncontrolling interest	13,703	20,042
Long-term debt, less current maturities	1,540,364	1,637,592
Total capitalization	3,101,999	3,143,900
Current liabilities:
Current maturities of long-term debt	19,865	19,192
Short-term debt	0	5,000
Accounts payable	129,258	167,988
Customer deposits	72,268	71,546
Income taxes payable	13,643	0
Accrued general taxes	42,249	44,339
Accrued interest	21,730	16,468
Deferred income taxes	7,031	0
Deferred purchased gas costs	44,754	0
Other current liabilities	143,882	145,584
Total current liabilities	494,680	470,117
Deferred income taxes and other credits:
Deferred income taxes and investment tax credits	722,718	723,688
Accumulated removal costs	301,000	304,000
Other deferred credits and other long-term liabilities	563,269	572,810
Total deferred income taxes and other credits	1,586,987	1,600,498
Total capitalization and liabilities	$ 5,183,666	$ 5,214,515

Condensed Consolidated Balance3

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Common stock, par	$ 1	$ 1
Common stock, authorized	60,000,000	60,000,000
Common stock, issued	47,375,398	46,523,184
Common stock, outstanding	47,375,398	46,523,184

Condensed Consolidated Statemen

Condensed Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Operating revenues:
Gas operating revenues	$ 219,420	$ 226,027	$ 1,059,178	$ 983,999	$ 1,457,266	$ 1,356,653
Construction revenues	285,976	206,448	719,042	510,025	948,637	675,728
Total operating revenues	505,396	432,475	1,778,220	1,494,024	2,405,903	2,032,381
Operating expenses:
Net cost of gas sold	64,268	72,987	427,045	362,349	570,052	480,608
Operations and maintenance	100,102	93,389	294,956	293,417	385,271	390,328
Depreciation and amortization	66,476	62,037	200,898	187,114	266,811	247,684
Taxes other than income taxes	11,652	11,835	37,063	34,256	50,059	45,786
Construction expenses	246,755	173,937	647,512	444,778	850,591	595,093
Total operating expenses	489,253	414,185	1,607,474	1,321,914	2,122,784	1,759,499
Operating income	16,143	18,290	170,746	172,110	283,119	272,882
Other income and (expenses):
Net interest deductions	(18,401)	(17,421)	(54,095)	(52,245)	(73,919)	(69,680)
Other income (deductions)	(3,660)	440	(1,226)	4,915	966	9,026
Total other income and (expenses)	(22,061)	(16,981)	(55,321)	(47,330)	(72,953)	(60,654)
Income (loss) before income taxes	(5,918)	1,309	115,425	124,780	210,166	212,228
Income tax expense (benefit)	(1,708)	(618)	42,693	42,529	78,537	72,788
Net income (loss)	(4,210)	1,927	72,732	82,251	131,629	139,440
Net income (loss) attributable to noncontrolling interests	524	(43)	534	(129)	685	(243)
Net income (loss) attributable to Southwest Gas Corporation	$ (4,734)	$ 1,970	$ 72,198	$ 82,380	$ 130,944	$ 139,683
Basic earnings (loss) per share	$ (0.10)	$ 0.04	$ 1.54	$ 1.77	$ 2.80	$ 3.01
Diluted earnings (loss) per share	(0.10)	0.04	1.53	1.76	2.77	2.98
Dividends declared per share	$ 0.405	$ 0.365	$ 1.215	$ 1.095	$ 1.580	$ 1.425
Average number of common shares outstanding	47,102	46,513	46,863	46,485	46,777	46,451
Average shares outstanding (assuming dilution)	0	46,966	47,261	46,928	47,194	46,904

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ (4,210)	$ 1,927	$ 72,732	$ 82,251	$ 131,629	$ 139,440
Defined benefit pension plans:
Net actuarial gain (loss)	0	0	0	0	(107,661)	62,214
Amortization of prior service cost	207	55	621	165	676	221
Amortization of net actuarial loss	5,329	3,667	15,987	11,000	19,654	16,297
Prior service cost	0	0	0	0	(4,130)	0
Regulatory adjustment	(4,828)	(3,210)	(14,484)	(9,630)	82,137	(72,176)
Net defined benefit pension plans	708	512	2,124	1,535	(9,324)	6,556
Forward-starting interest rate swaps:
Amounts reclassified into net income	519	518	1,556	1,555	2,074	2,074
Net forward-starting interest rate swaps	519	518	1,556	1,555	2,074	2,074
Foreign currency translation adjustments	(510)	0	(1,573)	0	(2,232)	0
Total other comprehensive income (loss), net of tax	717	1,030	2,107	3,090	(9,482)	8,630
Comprehensive income (loss)	(3,493)	2,957	74,839	85,341	122,147	148,070
Comprehensive income (loss) attributable to noncontrolling interests	504	(43)	479	(129)	608	(243)
Comprehensive income (loss) attributable to Southwest Gas Corporation	$ (3,997)	$ 3,000	$ 74,360	$ 85,470	$ 121,539	$ 148,313

Condensed Consolidated Stateme6

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
CASH FLOW FROM OPERATING ACTIVITIES:
Net income	$ 72,732	$ 82,251	$ 131,629	$ 139,440
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	200,898	187,114	266,811	247,684
Deferred income taxes	5,961	37,690	32,580	62,625
Changes in current assets and liabilities:
Accounts receivable, net of allowances	6,570	34,679	(31,792)	(29,187)
Accrued utility revenue	41,700	40,700	(200)	(700)
Deferred purchased gas costs	131,495	(60,101)	122,257	(92,535)
Accounts payable	(38,878)	(85,514)	5,137	(3,029)
Accrued taxes	(4,427)	(16,869)	(1,131)	(14,704)
Other current assets and liabilities	8,333	43,650	(11,938)	20,941
Gains on sale	(3,019)	(5,661)	(3,529)	(6,783)
Changes in undistributed stock compensation	2,119	4,612	5,480	6,126
AFUDC	(2,011)	(1,571)	(2,435)	(2,187)
Changes in other assets and deferred charges	(14,423)	(17,420)	(18,735)	(16,685)
Changes in other liabilities and deferred credits	5,348	18,344	2,783	28,569
Net cash provided by operating activities	412,398	261,904	496,917	339,575
CASH FLOW FROM INVESTING ACTIVITIES:
Construction expenditures and property additions	(336,569)	(293,276)	(440,191)	(403,115)
Acquisition of businesses, net of cash acquired	(9,261)	0	(199,758)	0
Restricted cash	785	0	2,018	0
Changes in customer advances	14,300	13,124	21,539	15,694
Miscellaneous inflows	11,593	9,780	13,424	11,838
Miscellaneous outflows	0	0	(1,400)	0
Net cash used in investing activities	(319,152)	(270,372)	(604,368)	(375,583)
CASH FLOW FROM FINANCING ACTIVITIES:
Issuance of common stock, net	35,419	419	35,405	608
Dividends paid	(55,060)	(49,295)	(72,040)	(64,592)
Issuance of long-term debt, net	123,816	37,719	355,325	285,336
Retirement of long-term debt	(143,325)	(21,528)	(260,952)	(28,272)
Change in credit facility and commercial paper	(53,000)	40,000	47,000	(100,000)
Change in short-term debt	(5,000)	0	0	(33,000)
Principal payments on capital lease obligations	(1,096)	0	(1,530)	0
Other	(504)	(759)	(1,002)	1,240
Net cash provided by (used in) financing activities	(98,750)	6,556	102,206	61,320
Effects of currency translation on cash and cash equivalents	(1,103)	0	(961)	0
Change in cash and cash equivalents	(6,607)	(1,912)	(6,206)	25,312
Cash and cash equivalents at beginning of period	39,566	41,077	39,165	13,853
Cash and cash equivalents at end of period	32,959	39,165	32,959	39,165
Supplemental information:
Interest paid, net of amounts capitalized	45,312	42,695	68,169	60,264
Income taxes paid	$ 39,856	$ 14,823	$ 49,280	$ 16,744

Nature of Operations and Basis

Nature of Operations and Basis of Presentation	9 Months Ended
	Sep. 30, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Operations and Basis of Presentation	Note 1 – Nature of Operations and Basis of Presentation Nature of Operations. Basis of Presentation. Centuri, through its subsidiaries, holds a 50% interest in W.S. Nicholls Western Construction LTD. (“Western”), a Canadian construction services company that is a variable interest entity. Centuri determined that it is not the primary beneficiary of the entity due to a shared-power structure; therefore, Centuri does not consolidate the entity and has recorded its investment, and results related thereto, using the equity method. The Company’s investment in Western is not significant in relation to its total assets included in the Condensed Consolidated Balance Sheets. Prepaids and other current assets. Cash and Cash Equivalents. Significant non-cash investing and financing activities for the natural gas operations segment included the following: Upon contract expiration, customer advances of approximately $2.8 million and $7 million, during the first nine months of 2015 and 2014, respectively, were applied as contributions toward utility construction activity and represent non-cash investing activity. Goodwill. Therefore, goodwill assigned to Brigadier is expected to be deductible for tax purposes, resulting in an after-tax value of $4.9 million. All other goodwill associated with the acquisition is not deductible for tax purposes. (In thousands of dollars) Natural Gas Construction Consolidated December 31, 2014 $ 10,095 $ 133,065 $ 143,160 Acquisition date adjustment — 1,380 1,380 Foreign currency translation adjustment — (14,656 ) (14,656 ) September 30, 2015 $ 10,095 $ 119,789 $ 129,884 Intercompany Transactions Note 3—Segment Information September 30, December 31, Centuri accounts receivable for services provided to Southwest $ 15,972 $ 9,169 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 Property and Investments. September 30, December 31, Centuri property and equipment $ 419 $ 405 Centuri accumulated provision for depreciation and amortization (209 ) (187 ) Net cash surrender value of COLI policies 97 99 Other property 12 10 Total $ 319 $ 327 Other Income (Deductions). Three Months Ended Nine Months Ended Twelve Months Ended September 30 September 30 September 30 2015 2014 2015 2014 2015 2014 Change in COLI policies $ (3,900 ) $ (300 ) $ (2,600 ) $ 2,900 $ (200 ) $ 7,200 Interest income 624 772 1,375 1,881 2,096 1,920 Foreign transaction gain (loss) (302 ) — (874 ) — (1,052 ) — Miscellaneous income and (expense) (82 ) (32 ) 873 134 122 (94 ) Total other income (deductions) $ (3,660 ) $ 440 $ (1,226 ) $ 4,915 $ 966 $ 9,026 Included 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, changes in the cash surrender values of COLI policies, as they progress towards the ultimate death benefits, are also recorded without tax consequences. Recently Issued Accounting Standards Updates. In August 2014, the FASB issued the update “Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern,” which requires management to assess a company’s ability to continue as a going concern and to provide related footnote disclosures in certain circumstances. Under the update, disclosures are required when conditions give rise to substantial doubt about a company’s ability to continue as a going concern within one year from the financial statement issuance date. The update is effective for the annual period ending after December 15, 2016, and all annual and interim periods thereafter. This update is not expected to have a material impact on the Company’s disclosures. In April 2015, the FASB issued the update “Interest—Imputation of Interest (Subtopic 835-30) Simplifying the Presentation of Debt Issuance Costs.” To simplify presentation of debt issuance costs, the amendments in this update require that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. The recognition and measurement guidance for debt issuance costs are not affected by the amendments in this update. Retrospective application of the update is required. The amendments in this update are effective for financial statements issued for fiscal years beginning after December 15, 2015, and interim periods within fiscal years beginning after December 15, 2016. Early adoption of the amendments in this update is permitted for financial statements that have not been previously issued. This update is not expected to have a material impact on the Company’s consolidated financial statements and disclosures.

Components of Net Periodic Bene

Components of Net Periodic Benefit Cost	9 Months Ended
	Sep. 30, 2015
Text Block [Abstract]
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. Net periodic benefit costs included in the table below are components of an overhead loading process associated with the cost of labor. The overhead process ultimately results in allocation of net periodic benefit costs to the same accounts to which productive labor is charged. As a result, net periodic benefit costs become components of various accounts, primarily operations and maintenance expense, net utility plant, and deferred charges and other assets. Qualified Retirement Plan Period Ended September 30, Three Months Nine Months Twelve Months 2015 2014 2015 2014 2015 2014 (Thousands of dollars) Service cost $ 6,281 $ 5,340 $ 18,842 $ 16,020 $ 24,182 $ 21,784 Interest cost 11,057 10,860 33,172 32,581 44,031 41,983 Expected return on plan assets (14,452 ) (13,336 ) (43,356 ) (40,007 ) (56,691 ) (52,467 ) Amortization of net actuarial loss 8,186 5,718 24,557 17,154 30,276 25,219 Net periodic benefit cost $ 11,072 $ 8,582 $ 33,215 $ 25,748 $ 41,798 $ 36,519 SERP Period Ended September 30, Three Months Nine Months Twelve Months 2015 2014 2015 2014 2015 2014 (Thousands of dollars) Service cost $ 80 $ 73 $ 240 $ 219 $ 313 $ 312 Interest cost 424 436 1,271 1,308 1,708 1,692 Amortization of net actuarial loss 323 196 970 588 1,165 830 Net periodic benefit cost $ 827 $ 705 $ 2,481 $ 2,115 $ 3,186 $ 2,834 PBOP Period Ended September 30, Three Months Nine Months Twelve Months 2015 2014 2015 2014 2015 2014 (Thousands of dollars) Service cost $ 410 $ 275 $ 1,231 $ 826 $ 1,506 $ 1,131 Interest cost 750 707 2,249 2,122 2,956 2,743 Expected return on plan assets (866 ) (816 ) (2,598 ) (2,448 ) (3,414 ) (3,154 ) Amortization of prior service costs 334 89 1,001 266 1,090 355 Amortization of net actuarial loss 86 — 259 — 259 236 Net periodic benefit cost $ 714 $ 255 $ 2,142 $ 766 $ 2,397 $ 1,311

Segment Information

Segment Information	9 Months Ended
	Sep. 30, 2015
Segment Reporting [Abstract]
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 Construction Total Three months ended September 30, 2015 Revenues from external customers $ 219,420 $ 255,088 $ 474,508 Intersegment revenues — 30,888 30,888 Total $ 219,420 $ 285,976 $ 505,396 Segment net income (loss) $ (18,939 ) $ 14,205 $ (4,734 ) Three months ended September 30, 2014 Revenues from external customers $ 226,027 $ 183,290 $ 409,317 Intersegment revenues — 23,158 23,158 Total $ 226,027 $ 206,448 $ 432,475 Segment net income (loss) $ (11,452 ) $ 13,422 $ 1,970 Natural Gas Construction Total Nine months ended September 30, 2015 Revenues from external customers $ 1,059,178 $ 645,289 $ 1,704,467 Intersegment revenues — 73,753 73,753 Total $ 1,059,178 $ 719,042 $ 1,778,220 Segment net income $ 59,325 $ 12,873 $ 72,198 Nine months ended September 30, 2014 Revenues from external customers $ 983,999 $ 438,409 $ 1,422,408 Intersegment revenues — 71,616 71,616 Total $ 983,999 $ 510,025 $ 1,494,024 Segment net income $ 62,945 $ 19,435 $ 82,380 Natural Gas Construction Total Twelve months ended September 30, 2015 Revenues from external customers $ 1,457,266 $ 854,312 $ 2,311,578 Intersegment revenues — 94,325 94,325 Total $ 1,457,266 $ 948,637 $ 2,405,903 Segment net income $ 113,252 $ 17,692 $ 130,944 Twelve months ended September 30, 2014 Revenues from external customers $ 1,356,653 $ 577,384 $ 1,934,037 Intersegment revenues — 98,344 98,344 Total $ 1,356,653 $ 675,728 $ 2,032,381 Segment net income $ 117,797 $ 21,886 $ 139,683

Derivatives and Fair Value Meas

Derivatives and Fair Value Measurements	9 Months Ended
	Sep. 30, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivatives and Fair Value Measurements	Note 4 – Derivatives and Fair Value Measurements Derivatives. The fixed-price contracts and Swaps are utilized by Southwest under its volatility mitigation programs to effectively fix the price on a portion (up to 25% in the Arizona and California jurisdictions) 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 2015 through March 2017. 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, December 31, Contract notional amounts 8,192 5,105 In late 2013, the Company suspended further Swaps and fixed-price purchases pursuant to the Volatility Mitigation Program (“VMP”) for its Nevada service territories. The decision did not impact previously executed purchase arrangements. Agreements, under the Nevada VMP, made prior to the suspension, terminated following the March 2015 delivery month. The Company, along with its regulators, will continue to evaluate this strategy in light of prevailing or anticipated changing market conditions. Southwest does not utilize derivative financial instruments for speculative purposes, nor does it have trading operations. The following table sets forth the gains and (losses) recognized on the Company’s Swaps (derivatives) for the three-, nine-, and twelve-month periods ended September 30, 2015 and 2014 and their location in the Condensed Consolidated Statements of Income: Gains (losses) recognized in income for derivatives not designated as hedging instruments: (Thousands of dollars) Location of Gain or (Loss) Three Months Ended Nine Months Ended Twelve Months Ended September 30 September 30 September 30 Instrument 2015 2014 2015 2014 2015 2014 Swaps Net cost of gas sold $ (3,282 ) $ (2,277 ) $ (4,689 ) $ 3,630 $ (10,682 ) $ 7,552 Swaps Net cost of gas sold 3,282 * 2,277 * 4,689 * (3,630 )* 10,682 * (7,552 )* Total $ — $ — $ — $ — $ — $ — * Represents the impact of regulatory deferral accounting treatment under U.S. GAAP for rate-regulated entities. No gains (losses) were recognized in income or other comprehensive income during the periods presented for derivatives designated as cash flow hedging instruments. Previously, Southwest entered into two forward-starting interest rate swaps (“FSIRS”), both of which were designated cash flow hedges, to partially hedge the risk of interest rate variability during the period leading up to the issuance of debt. The first FSIRS terminated in December 2010. The second FSIRS terminated in March 2012. Losses on both FSIRS are being amortized over ten-year periods from Accumulated other comprehensive income (loss) and into interest expense. The following table sets forth the fair values of the Company’s Swaps and their location in the Condensed Consolidated Balance Sheets (thousands of dollars): Fair values of derivatives not designated as hedging instruments: September 30, 2015 Asset Derivatives Liability Derivatives Net Total Instrument Balance Sheet Location Swaps Other current liabilities $ — $ (3,425 ) $ (3,425 ) Swaps Other deferred credits — (1,462 ) (1,462 ) Total $ — $ (4,887 ) $ (4,887 ) December 31, 2014 Asset Derivatives Liability Derivatives Net Total Instrument Balance Sheet Location Swaps Other current liabilities $ — $ (5,062 ) $ (5,062 ) Swaps Other deferred credits — (363 ) (363 ) Total $ — $ (5,425 ) $ (5,425 ) 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. The Company had no outstanding collateral associated with the Swaps during either period shown in the above table. 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 mature, 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, 2015 September 30, 2015 September 30, 2015 Paid to counterparties $ 568 $ 5,228 $ 5,971 Received from counterparties $ — $ — $ 120 The following table details the regulatory assets/(liabilities) offsetting the derivatives at fair value in the Condensed Consolidated Balance Sheets (thousands of dollars). September 30, 2015 Instrument Balance Sheet Location Net Total Swaps Prepaids and other current assets $ 3,425 Swaps Deferred charges and other assets 1,462 December 31, 2014 Instrument Balance Sheet Location Net Total Swaps Prepaids and other current assets $ 5,062 Swaps Deferred charges and other assets 363 Fair Value Measurements. 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, December 31, Liabilities at fair value: Other current liabilities—Swaps $ (3,425 ) $ (5,062 ) Other deferred credits—Swaps (1,462 ) (363 ) Net Assets (Liabilities) $ (4,887 ) $ (5,425 ) No financial assets or liabilities accounted for at fair value fell within Level 1 (quoted prices in active markets for identical financial assets) or Level 3 (significant unobservable inputs) of the fair value hierarchy. With regard to the fair values of assets associated with the Company’s pension and postretirement benefit plans, asset values were last updated as required as of December 2014. Refer to Note 9 – Pension and Other Post Retirement Benefits in the 2014 Annual Report to Shareholders on Form 10-K.

Common Stock

Common Stock	9 Months Ended
	Sep. 30, 2015
Text Block [Abstract]
Common Stock	Note 5 – Common Stock On March 10, 2015, the Company filed with the Securities Exchange Commission (“SEC”) an automatic shelf registration statement on Form S-3 (File No. 333-202633), which became effective upon filing, for the offer and sale of up to $100,000,000 of the Company’s common stock from time to time in at-the-market offerings under the prospectus included therein and in accordance with the Sales Agency Agreement, dated March 10, 2015, between the Company and BNY Mellon Capital Markets, LLC (the “Equity Shelf Program”). During the three months ending September 30, 2015, the Company sold, through the continuous equity offering program with BNY Mellon Capital Markets, LLC as agent, an aggregate of 272,716 shares of the Company’s common stock in the open market at a weighted average price of $54.12 per share, resulting in proceeds to the Company of $14,610,439, net of $147,579 in agent commissions. For the nine months ended September 30, 2015, the Company sold an aggregate of 645,225 shares of common stock under this program resulting in proceeds to the Company of $35,167,584, net of $355,228 in agent commissions. As of September 30, 2015, the Company had up to $64,477,188 of common stock available for sale under the program. Net proceeds from the sale of shares of common stock under the Equity Shelf Program are intended for general corporate purposes, including the acquisition of property for the construction, completion, extension or improvement of pipeline systems and facilities located in and around the communities Southwest serves. In addition, during the nine months ended September 30, 2015, the Company issued approximately 207,000 shares of common stock through the Stock Incentive Plan, Restricted Stock/Unit Plan, and Management Incentive Plan.

Long-Term Debt

Long-Term Debt	9 Months Ended
	Sep. 30, 2015
Debt Disclosure [Abstract]
Long-Term Debt	Note 6 – Long-Term Debt Carrying amounts of the Company’s long-term debt and their related estimated fair values as of September 30, 2015 and December 31, 2014 are disclosed in the following table. The fair values of the revolving credit facility (including commercial paper) and the variable-rate Industrial Development Revenue Bonds (“IDRBs”) approximate their carrying values, as they are repaid quickly (in the case of credit facility borrowings) and have interest rates that reset frequently. They are categorized as Level 1 (quoted prices for identical financial instruments) within the three-level September 30, 2015 December 31, 2014 Carrying Market Carrying Market (Thousands of dollars) Debentures: Notes, 4.45%, due 2020 $ 125,000 $ 132,769 $ 125,000 $ 133,403 Notes, 6.1%, due 2041 125,000 147,451 125,000 157,290 Notes, 3.875%, due 2022 250,000 263,023 250,000 262,030 Notes, 4.875%, due 2043 250,000 266,370 250,000 280,903 8% Series, due 2026 75,000 99,380 75,000 102,296 Medium-term notes, 7.59% series, due 2017 25,000 26,662 25,000 27,573 Medium-term notes, 7.78% series, due 2022 25,000 30,621 25,000 31,144 Medium-term notes, 7.92% series, due 2027 25,000 32,726 25,000 33,695 Medium-term notes, 6.76% series, due 2027 7,500 8,917 7,500 9,156 Unamortized discount (4,957 ) (5,223 ) 902,543 902,277 Revolving credit facility and commercial paper 97,000 97,000 150,000 150,000 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: 5.25% 2003 Series D, due 2038 — — 20,000 20,277 5.00% 2004 Series B, due 2033 — — 31,200 31,223 4.85% 2005 Series A, due 2035 100,000 100,415 100,000 100,071 4.75% 2006 Series A, due 2036 24,855 25,089 24,855 25,399 Unamortized discount (1,539 ) (1,943 ) 323,316 374,112 Centuri secured revolving credit and term loan facility 208,787 209,213 199,267 200,341 Centuri other debt obligations 28,583 28,868 31,128 31,127 1,560,229 1,656,784 Less: current maturities (19,865 ) (19,192 ) Long-term debt, less current maturities $ 1,540,364 $ 1,637,592 In March 2015, the Company amended its $300 million credit facility. The facility was previously scheduled to expire in March 2019 and was extended to March 2020. The Company will continue to use $150 million of the facility as long-term debt and the remaining $150 million for working capital purposes. Interest rates for the credit facility are calculated at either the London Interbank Offered Rate (“LIBOR”) or an “alternate base rate,” plus in each case an applicable margin that is determined based on the Company’s senior unsecured debt rating. At September 30, 2015, the applicable margin is 1% for loans bearing interest with reference to LIBOR and 0% for loans bearing interest with reference to the alternative base rate. At September 30, 2015, $47 million was outstanding on the credit facility and $50 million was outstanding on the commercial paper program. In May 2015, the Company redeemed at par the $31.2 million 5.00% 2004 Series B IDRBs originally due in 2033. The Company facilitated the redemption primarily from cash on hand and borrowings under its $300 million credit facility. In September 2015, the Company redeemed at par the $20 million 5.25% 2003 Series D IDRBs originally due in 2038. The Company facilitated the redemption primarily from cash on hand and borrowings under its $300 million credit facility. Centuri has a $300 million secured revolving credit and term loan facility that is scheduled to expire in October 2019. At September 30, 2015, $209 million in borrowings were outstanding on the Centuri facility. Centuri assets securing the facility at September 30, 2015 totaled $557 million.

Equity, Other Comprehensive Inc

Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income	9 Months Ended
	Sep. 30, 2015
Equity [Abstract]
Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income	Note 7 – Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income The table below provides details of activity in equity and the redeemable noncontrolling interest during the nine months ended September 30, 2015. Southwest Gas Corporation Equity Additional Paid-in Capital Accumulated Comprehensive Income (Loss) Redeemable Interest (Temporary Common Stock Retained Non-controlling (In thousands except per share amounts) Shares Amount Total DECEMBER 31, 2014 46,523 $ 48,153 $ 851,381 $ (50,175 ) $ 639,164 $ (2,257 ) $ 1,486,266 $ 20,042 Common stock issuances 852 852 37,467 38,319 Net income (loss) 72,198 80 72,278 454 Redemption value adjustments 5,777 961 6,738 (6,738 ) Foreign currency exchange translation adj. (1,518 ) (1,518 ) (55 ) Other comprehensive income (loss): Net actuarial gain (loss) arising during period, less amortization of unamortized benefit plan cost, net of tax 2,124 2,124 Amounts reclassified to net income, net of tax (FSIRS) 1,556 1,556 Dividends declared Common: $1.215 per share (57,831 ) (57,831 ) SEPTEMBER 30, 2015 47,375 $ 49,005 $ 894,625 $ (48,013 ) $ 654,492 $ (2,177 ) $ 1,547,932 $ 13,703 The following information provides insight into amounts impacting Other Comprehensive Income (Loss), both before and after-tax, within the Condensed Consolidated Statements of Comprehensive Income, which also impact Accumulated Other Comprehensive Income in the Company’s Condensed Consolidated Balance Sheets and the associated column in the equity table above. See Note 4 – Derivatives and Fair Value Measurements Related Tax Effects Allocated to Each Component of Other Comprehensive Income (Loss) (Thousands of dollars) Three Months Ended September 30, 2015 Three Months Ended September 30, 2014 Before- Tax Net-of- Before- Tax Net-of- Defined benefit pension plans: Amortization of prior service cost $ 334 $ (127 ) $ 207 $ 89 $ (34 ) $ 55 Amortization of net actuarial (gain)/loss 8,595 (3,266 ) 5,329 5,914 (2,247 ) 3,667 Regulatory adjustment (7,787 ) 2,959 (4,828 ) (5,178 ) 1,968 (3,210 ) Pension plans other comprehensive income (loss) 1,142 (434 ) 708 825 (313 ) 512 FSIRS (designated hedging activities): Amounts reclassified into net income 836 (317 ) 519 836 (318 ) 518 FSIRS other comprehensive income 836 (317 ) 519 836 (318 ) 518 Foreign currency translation adjustments: Translation adjustments (510 ) — (510 ) — — — Foreign currency other comprehensive income (loss) (510 ) — (510 ) — — — Total other comprehensive income (loss) $ 1,468 $ (751 ) $ 717 $ 1,661 $ (631 ) $ 1,030 Nine Months Ended September 30, 2015 Nine Months Ended September 30, 2014 Before- Tax Tax Net-of- Tax Before- Tax Tax Net-of- Defined benefit pension plans: Amortization of prior service cost $ 1,001 $ (380 ) $ 621 $ 266 $ (101 ) $ 165 Amortization of net actuarial (gain)/loss 25,786 (9,799 ) 15,987 17,742 (6,742 ) $ 11,000 Regulatory adjustment (23,361 ) 8,877 (14,484 ) (15,533 ) 5,903 (9,630 ) Pension plans other comprehensive income (loss) 3,426 (1,302 ) 2,124 2,475 (940 ) 1,535 FSIRS (designated hedging activities): Amounts reclassifed into net income 2,508 (952 ) 1,556 2,509 (954 ) 1,555 FSIRS other comprehensive income 2,508 (952 ) 1,556 2,509 (954 ) 1,555 Foreign currency translation adjustments: Translation adjustments (1,573 ) — (1,573 ) — — — Foreign currency other comprehensive income (loss) (1,573 ) — (1,573 ) — — — Total other comprehensive income (loss) $ 4,361 $ (2,254 ) $ 2,107 $ 4,984 $ (1,894 ) $ 3,090 Twelve Months Ended September 30, 2015 Twelve Months Ended September 30, 2014 Before- Tax Tax Net-of- Tax Before- Tax Tax Net-of- Defined benefit pension plans: Net actuarial gain (loss) $ (173,646 ) $ 65,985 $ (107,661 ) $ 100,345 $ (38,131 ) $ 62,214 Amortization of prior service cost 1,090 (414 ) 676 355 (134 ) 221 Amortization of net actuarial (gain)/loss 31,700 (12,046 ) 19,654 26,285 (9,988 ) 16,297 Prior service cost (6,661 ) 2,531 (4,130 ) — — — Regulatory adjustment 132,480 (50,343 ) 82,137 (116,412 ) 44,236 (72,176 ) Pension plans other comprehensive income (loss) (15,037 ) 5,713 (9,324 ) 10,573 (4,017 ) 6,556 FSIRS (designated hedging activities): Amounts reclassified into net income 3,344 (1,270 ) 2,074 3,345 (1,271 ) 2,074 FSIRS other comprehensive income (loss) 3,344 (1,270 ) 2,074 3,345 (1,271 ) 2,074 Foreign currency translation adjustments: Translation adjustments (2,232 ) — (2,232 ) — — — Foreign currency other comprehensive income (loss) (2,232 ) — (2,232 ) — — — Total other comprehensive income (loss) $ (13,925 ) $ 4,443 $ (9,482 ) $ 13,918 $ (5,288 ) $ 8,630 (1) Tax amounts are calculated using a 38% rate. The Company has elected to indefinitely reinvest the earnings of Centuri’s Canadian subsidiaries in Canada, thus preventing deferred taxes on such earnings. As a result of this assertion, the Company is not recognizing any tax effect or presenting a tax expense or benefit for the currency translation adjustment amount reported in Other Comprehensive Income, as repatriation of earnings is not anticipated. Approximately $2.1 million of realized losses (net of tax) related to the FSIRS, reported in Accumulated other comprehensive income (“AOCI”) at September 30, 2015, will be reclassified into interest expense within the next 12 months, as the related interest payments on long-term debt occur. The following table represents a rollforward of AOCI, presented on the Company’s Condensed Consolidated Balance Sheets: AOCI—Rollforward (Thousands of dollars) Defined Benefit Plans FSIRS Foreign Currency Items Before-Tax Tax After-Tax Before-Tax Tax After-Tax Before-Tax Tax After-Tax AOCI Beginning Balance AOCI December 31, 2014 $ (57,211 ) $ 21,740 $ (35,471 ) $ (22,688 ) $ 8,621 $ (14,067 ) $ (637 ) $ — $ (637 ) $ (50,175 ) Translation adjustments — — — — — — (1,573 ) — (1,573 ) (1,573 ) Other comprehensive income before reclassifications — — — — — — (1,573 ) — (1,573 ) (1,573 ) FSIRS amounts reclassified from AOCI (1) — — — 2,508 (952 ) 1,556 — — — 1,556 Amortization of prior service cost (2) 1,001 (380 ) 621 — — — — — — 621 Amortization of net actuarial loss (2) 25,786 (9,799 ) 15,987 — — — — — — 15,987 Regulatory adjustment (3) (23,361 ) 8,877 (14,484 ) — — — — — — (14,484 ) Net current period other comprehensive income (loss) 3,426 (1,302 ) 2,124 2,508 (952 ) 1,556 (1,573 ) — (1,573 ) 2,107 Less: Translation adjustment attributable to redeemable noncontrolling interest — — — — — — (55 ) — (55 ) (55 ) Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation 3,426 (1,302 ) 2,124 2,508 (952 ) 1,556 (1,518 ) — (1,518 ) 2,162 Ending Balance AOCI September 30, 2015 $ (53,785 ) $ 20,438 $ (33,347 ) $ (20,180 ) $ 7,669 $ (12,511 ) $ (2,155 ) $ — $ (2,155 ) $ (48,013 ) (1) The FSIRS reclassification amounts are included in the Net interest deductions line item on the Condensed Consolidated Statements of Income. (2) These AOCI components are included in the computation of net periodic benefit cost (see Note 2 – Components of Net Periodic Benefit Cost (3) The regulatory adjustment represents the portion of the activity above that is expected to be recovered through rates in the future (the related regulatory asset is included in the Deferred charges and other assets line item on the Condensed Consolidated Balance Sheets). The following table represents amounts (before income tax impacts) associated with defined benefit plans, and included in AOCI (in the table above), that have not yet been recognized in net periodic benefit cost: Amounts Recognized in AOCI (Before Tax) (Thousands of dollars) September December Net actuarial (loss) gain $ (413,345 ) $ (439,131 ) Prior service cost (7,372 ) (8,373 ) Less: amount recognized in regulatory assets 366,932 390,293 Recognized in AOCI $ (53,785 ) $ (57,211 )

Acquisition of Construction Ser

Acquisition of Construction Services Businesses	9 Months Ended
	Sep. 30, 2015
Business Combinations [Abstract]
Acquisition of Construction Services Businesses	Note 8 – Acquisition of Construction Services Businesses In October 2014, the Company, through its subsidiaries, completed the acquisition of three privately held, affiliated construction businesses. See the Company’s 2014 Form 10-K and the first quarter 2015 Form 10-Q for additional information about this acquisition. While refinements were made to the estimated fair values of assets acquired and liabilities assumed during the first quarter of 2015, no subsequent adjustments were made to acquisition-date values. The final purchase accounting has been completed.

Construction Services Redeemabl

Construction Services Redeemable Noncontrolling Interest	9 Months Ended
	Sep. 30, 2015
Noncontrolling Interest [Abstract]
Construction Services Redeemable Noncontrolling Interest	Note 9 – Construction Services Redeemable Noncontrolling Interest At the close of the acquisition discussed above, previous owners of the acquired companies retained an approximate 10% equity interest in the Canadian-specific businesses. The agreement, associated with that approximate 10% equity interest, provided special dividend rights which entitled the sellers, as holders, to dividends equal to 3.4% of dividends paid at the level of Centuri, and subject to certain conditions, such interests could become exchangeable for a 3.4% equity interest in Centuri. In consideration of the underlying exchange rights of the original agreement, earnings attribution by Centuri to the previous owners has also occurred in an amount equivalent to 3.4% of Centuri earnings since October 2014. During the third quarter of 2015, the sellers formally exercised their exchange rights under the terms of that original agreement. No new rights were conveyed to the noncontrolling parties as a result of the exchange and no new consideration was involved. The ability of the sellers to redeem their holdings for cash at specified dates remains intact. The previous owners may exit their investment retained by requiring the purchase of a portion of their interest commencing July 2017 and in incremental amounts each anniversary date thereafter. The shares subject to the election cumulate (if earlier elections are not made) such that 100% of their interest retained is subject to the election beginning in July 2022. Due to the continued ability of the noncontrolling parties to redeem their interest for cash, their interest continues to be presented on the Company’s Condensed Consolidated Balance Sheet at September 30, 2015 as a Redeemable noncontrolling interest, a category of mezzanine equity (temporary equity), in accordance with SEC guidance. However, that interest, previously associated with the Canadian businesses, is now formally an interest in Centuri. Significant changes in the value of the redeemable noncontrolling interest are recognized as they occur, and the carrying value is adjusted as necessary at each reporting date. Guidance by the SEC indicates that downward adjustments in the value of redeemable noncontrolling interests are only permitted to the extent that upward adjustments in value were previously recognized. A floor for the noncontrolling interest was originally set at the acquisition date (in October 2014). However, U.S. GAAP generally views changes in ownership interest, where the parent retains its controlling interest, as an equity transaction, whereby the carrying amount of the noncontrolling interest is adjusted to reflect the change in ownership interest in the subsidiary. In connection with the exchange rights being exercised during the third quarter, an updated valuation was conducted. A significant decrease in the value of the redeemable noncontrolling interest was recognized, due in part to the exchange option no longer being subject to probability estimates. In light of the U.S. GAAP requirement to adjust the carrying amount, a new floor has been set for the redeemable noncontrolling interest at the exchange date, with a corresponding adjustment (approximately $6 million) made to additional paid in capital of the Company. Future adjustments to the redemption value are not permitted below the new floor. The following depicts impacts to the balance of the redeemable noncontrolling interest between the indicated periods. Redeemable (Thousands of dollars): Balance, December 31, 2014 $ 20,042 Net income attributable to redeemable noncontrolling interest 454 Foreign currency exchange translation adjustment (55 ) Adjustment to redemption value (6,738 ) Balance, September 30, 2015 $ 13,703 The redemption value of the redeemable noncontrolling interest utilizes a market approach to determine a construction services enterprise value. Potential guideline publicly traded companies have been identified by using a selection criteria, including actively traded equities, their financial solvency, and other factors. Once the guideline companies are determined, enterprise value is calculated using a weighted approach of projected earnings before interest expense and taxes (“EBIT”) and earnings before interest expense, taxes, and depreciation and amortization expense (“EBITDA”). After an estimated fair value is determined, it is multiplied by 3.4%. A discount is then applied due to limitations of the nonpublic noncontrolling interest being valued. Prior to the exchange rights being exercised in the third quarter of 2015, a Monte Carlo simulation methodology was used to assign a value to the redeemable noncontrolling interest. Each quarter, market changes in the guideline companies are considered and the weighted approach to projected EBIT and EBITDA, in relation to the guideline companies, is re-evaluated to determine if value changes are necessary at each quarterly reporting date.

Nature of Operations and Basi16

Nature of Operations and Basis of Presentation (Policies)	9 Months Ended
	Sep. 30, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Operations	Nature of Operations.
Basis of Presentation	Basis of Presentation. Centuri, through its subsidiaries, holds a 50% interest in W.S. Nicholls Western Construction LTD. (“Western”), a Canadian construction services company that is a variable interest entity. Centuri determined that it is not the primary beneficiary of the entity due to a shared-power structure; therefore, Centuri does not consolidate the entity and has recorded its investment, and results related thereto, using the equity method. The Company’s investment in Western is not significant in relation to its total assets included in the Condensed Consolidated Balance Sheets.
Prepaids and Other Current Assets	Prepaids and other current assets.
Cash and Cash Equivalents	Cash and Cash Equivalents. Significant non-cash investing and financing activities for the natural gas operations segment included the following: Upon contract expiration, customer advances of approximately $2.8 million and $7 million, during the first nine months of 2015 and 2014, respectively, were applied as contributions toward utility construction activity and represent non-cash investing activity.
Goodwill	Goodwill. Therefore, goodwill assigned to Brigadier is expected to be deductible for tax purposes, resulting in an after-tax value of $4.9 million. All other goodwill associated with the acquisition is not deductible for tax purposes. (In thousands of dollars) Natural Gas Construction Consolidated December 31, 2014 $ 10,095 $ 133,065 $ 143,160 Acquisition date adjustment — 1,380 1,380 Foreign currency translation adjustment — (14,656 ) (14,656 ) September 30, 2015 $ 10,095 $ 119,789 $ 129,884
Intercompany Transactions	Intercompany Transactions Note 3—Segment Information September 30, December 31, Centuri accounts receivable for services provided to Southwest $ 15,972 $ 9,169 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 Property and Investments	Other Property and Investments. September 30, December 31, Centuri property and equipment $ 419 $ 405 Centuri accumulated provision for depreciation and amortization (209 ) (187 ) Net cash surrender value of COLI policies 97 99 Other property 12 10 Total $ 319 $ 327
Other Income (Deductions)	Other Income (Deductions). Three Months Ended Nine Months Ended Twelve Months Ended September 30 September 30 September 30 2015 2014 2015 2014 2015 2014 Change in COLI policies $ (3,900 ) $ (300 ) $ (2,600 ) $ 2,900 $ (200 ) $ 7,200 Interest income 624 772 1,375 1,881 2,096 1,920 Foreign transaction gain (loss) (302 ) — (874 ) — (1,052 ) — Miscellaneous income and (expense) (82 ) (32 ) 873 134 122 (94 ) Total other income (deductions) $ (3,660 ) $ 440 $ (1,226 ) $ 4,915 $ 966 $ 9,026 Included 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, changes in the cash surrender values of COLI policies, as they progress towards the ultimate death benefits, are also recorded without tax consequences.
Recently Issued Accounting Standards Updates	Recently Issued Accounting Standards Updates. In August 2014, the FASB issued the update “Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern,” which requires management to assess a company’s ability to continue as a going concern and to provide related footnote disclosures in certain circumstances. Under the update, disclosures are required when conditions give rise to substantial doubt about a company’s ability to continue as a going concern within one year from the financial statement issuance date. The update is effective for the annual period ending after December 15, 2016, and all annual and interim periods thereafter. This update is not expected to have a material impact on the Company’s disclosures. In April 2015, the FASB issued the update “Interest—Imputation of Interest (Subtopic 835-30) Simplifying the Presentation of Debt Issuance Costs.” To simplify presentation of debt issuance costs, the amendments in this update require that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. The recognition and measurement guidance for debt issuance costs are not affected by the amendments in this update. Retrospective application of the update is required. The amendments in this update are effective for financial statements issued for fiscal years beginning after December 15, 2015, and interim periods within fiscal years beginning after December 15, 2016. Early adoption of the amendments in this update is permitted for financial statements that have not been previously issued. This update is not expected to have a material impact on the Company’s consolidated financial statements and disclosures.

Nature of Operations and Basi17

Nature of Operations and Basis of Presentation (Tables)	9 Months Ended
	Sep. 30, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Goodwill	(In thousands of dollars) Natural Gas Construction Consolidated December 31, 2014 $ 10,095 $ 133,065 $ 143,160 Acquisition date adjustment — 1,380 1,380 Foreign currency translation adjustment — (14,656 ) (14,656 ) September 30, 2015 $ 10,095 $ 119,789 $ 129,884
Intercompany Transactions	Centuri’s accounts receivable for these services are presented in the table below (thousands of dollars): September 30, December 31, Centuri accounts receivable for services provided to Southwest $ 15,972 $ 9,169
Schedule of Other Property and Investments	Other Property and Investments. September 30, December 31, Centuri property and equipment $ 419 $ 405 Centuri accumulated provision for depreciation and amortization (209 ) (187 ) Net cash surrender value of COLI policies 97 99 Other property 12 10 Total $ 319 $ 327
Other Income (Deductions)	The following table provides the composition of significant items included in Other income (deductions) in the condensed consolidated statements of income (thousands of dollars): Three Months Ended Nine Months Ended Twelve Months Ended September 30 September 30 September 30 2015 2014 2015 2014 2015 2014 Change in COLI policies $ (3,900 ) $ (300 ) $ (2,600 ) $ 2,900 $ (200 ) $ 7,200 Interest income 624 772 1,375 1,881 2,096 1,920 Foreign transaction gain (loss) (302 ) — (874 ) — (1,052 ) — Miscellaneous income and (expense) (82 ) (32 ) 873 134 122 (94 ) Total other income (deductions) $ (3,660 ) $ 440 $ (1,226 ) $ 4,915 $ 966 $ 9,026

Components of Net Periodic Be18

Components of Net Periodic Benefit Cost (Tables)	9 Months Ended
	Sep. 30, 2015
Text Block [Abstract]
Schedule of Components of Net Periodic Benefit Costs	As a result, net periodic benefit costs become components of various accounts, primarily operations and maintenance expense, net utility plant, and deferred charges and other assets. Qualified Retirement Plan Period Ended September 30, Three Months Nine Months Twelve Months 2015 2014 2015 2014 2015 2014 (Thousands of dollars) Service cost $ 6,281 $ 5,340 $ 18,842 $ 16,020 $ 24,182 $ 21,784 Interest cost 11,057 10,860 33,172 32,581 44,031 41,983 Expected return on plan assets (14,452 ) (13,336 ) (43,356 ) (40,007 ) (56,691 ) (52,467 ) Amortization of net actuarial loss 8,186 5,718 24,557 17,154 30,276 25,219 Net periodic benefit cost $ 11,072 $ 8,582 $ 33,215 $ 25,748 $ 41,798 $ 36,519 SERP Period Ended September 30, Three Months Nine Months Twelve Months 2015 2014 2015 2014 2015 2014 (Thousands of dollars) Service cost $ 80 $ 73 $ 240 $ 219 $ 313 $ 312 Interest cost 424 436 1,271 1,308 1,708 1,692 Amortization of net actuarial loss 323 196 970 588 1,165 830 Net periodic benefit cost $ 827 $ 705 $ 2,481 $ 2,115 $ 3,186 $ 2,834 PBOP Period Ended September 30, Three Months Nine Months Twelve Months 2015 2014 2015 2014 2015 2014 (Thousands of dollars) Service cost $ 410 $ 275 $ 1,231 $ 826 $ 1,506 $ 1,131 Interest cost 750 707 2,249 2,122 2,956 2,743 Expected return on plan assets (866 ) (816 ) (2,598 ) (2,448 ) (3,414 ) (3,154 ) Amortization of prior service costs 334 89 1,001 266 1,090 355 Amortization of net actuarial loss 86 — 259 — 259 236 Net periodic benefit cost $ 714 $ 255 $ 2,142 $ 766 $ 2,397 $ 1,311

Segment Information (Tables)

Segment Information (Tables)	9 Months Ended
	Sep. 30, 2015
Segment Reporting [Abstract]
Schedule of Segment Reporting Information	The following tables present revenues from external customers, intersegment revenues, and segment net income (thousands of dollars): Natural Gas Construction Total Three months ended September 30, 2015 Revenues from external customers $ 219,420 $ 255,088 $ 474,508 Intersegment revenues — 30,888 30,888 Total $ 219,420 $ 285,976 $ 505,396 Segment net income (loss) $ (18,939 ) $ 14,205 $ (4,734 ) Three months ended September 30, 2014 Revenues from external customers $ 226,027 $ 183,290 $ 409,317 Intersegment revenues — 23,158 23,158 Total $ 226,027 $ 206,448 $ 432,475 Segment net income (loss) $ (11,452 ) $ 13,422 $ 1,970 Natural Gas Construction Total Nine months ended September 30, 2015 Revenues from external customers $ 1,059,178 $ 645,289 $ 1,704,467 Intersegment revenues — 73,753 73,753 Total $ 1,059,178 $ 719,042 $ 1,778,220 Segment net income $ 59,325 $ 12,873 $ 72,198 Nine months ended September 30, 2014 Revenues from external customers $ 983,999 $ 438,409 $ 1,422,408 Intersegment revenues — 71,616 71,616 Total $ 983,999 $ 510,025 $ 1,494,024 Segment net income $ 62,945 $ 19,435 $ 82,380 Natural Gas Construction Total Twelve months ended September 30, 2015 Revenues from external customers $ 1,457,266 $ 854,312 $ 2,311,578 Intersegment revenues — 94,325 94,325 Total $ 1,457,266 $ 948,637 $ 2,405,903 Segment net income $ 113,252 $ 17,692 $ 130,944 Twelve months ended September 30, 2014 Revenues from external customers $ 1,356,653 $ 577,384 $ 1,934,037 Intersegment revenues — 98,344 98,344 Total $ 1,356,653 $ 675,728 $ 2,032,381 Segment net income $ 117,797 $ 21,886 $ 139,683

Derivatives and Fair Value Me20

Derivatives and Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Notional Amounts under Swaps Contracts	The differential is calculated based on the notional amounts under the contracts, which are detailed in the table below (thousands of dekatherms): September 30, December 31, Contract notional amounts 8,192 5,105
Amount of Gain or Losses Recognized in Income on Derivatives	The following table sets forth the gains and (losses) recognized on the Company’s Swaps (derivatives) for the three-, nine-, and twelve-month periods ended September 30, 2015 and 2014 and their location in the Condensed Consolidated Statements of Income: Gains (losses) recognized in income for derivatives not designated as hedging instruments: (Thousands of dollars) Location of Gain or (Loss) Three Months Ended Nine Months Ended Twelve Months Ended September 30 September 30 September 30 Instrument 2015 2014 2015 2014 2015 2014 Swaps Net cost of gas sold $ (3,282 ) $ (2,277 ) $ (4,689 ) $ 3,630 $ (10,682 ) $ 7,552 Swaps Net cost of gas sold 3,282 * 2,277 * 4,689 * (3,630 )* 10,682 * (7,552 )* Total $ — $ — $ — $ — $ — $ — * Represents the impact of regulatory deferral accounting treatment under U.S. GAAP for rate-regulated entities.
Fair Values of Swaps in Condensed Consolidated Balance Sheets	The following table sets forth the fair values of the Company’s Swaps and their location in the Condensed Consolidated Balance Sheets (thousands of dollars): Fair values of derivatives not designated as hedging instruments: September 30, 2015 Asset Derivatives Liability Derivatives Net Total Instrument Balance Sheet Location Swaps Other current liabilities $ — $ (3,425 ) $ (3,425 ) Swaps Other deferred credits — (1,462 ) (1,462 ) Total $ — $ (4,887 ) $ (4,887 ) December 31, 2014 Asset Derivatives Liability Derivatives Net Total Instrument Balance Sheet Location Swaps Other current liabilities $ — $ (5,062 ) $ (5,062 ) Swaps Other deferred credits — (363 ) (363 ) Total $ — $ (5,425 ) $ (5,425 )
Paid to and Received from Counterparties for Settlements of Matured Swaps	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, 2015 September 30, 2015 September 30, 2015 Paid to counterparties $ 568 $ 5,228 $ 5,971 Received from counterparties $ — $ — $ 120
Regulatory Assets/Liabilities Offsetting Derivatives at Fair Value in Condensed Consolidated Balance Sheets	The following table details the regulatory assets/(liabilities) offsetting the derivatives at fair value in the Condensed Consolidated Balance Sheets (thousands of dollars). September 30, 2015 Instrument Balance Sheet Location Net Total Swaps Prepaids and other current assets $ 3,425 Swaps Deferred charges and other assets 1,462 December 31, 2014 Instrument Balance Sheet Location Net Total Swaps Prepaids and other current assets $ 5,062 Swaps Deferred charges and other assets 363
Significant Other Observable Inputs	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, December 31, Liabilities at fair value: Other current liabilities—Swaps $ (3,425 ) $ (5,062 ) Other deferred credits—Swaps (1,462 ) (363 ) Net Assets (Liabilities) $ (4,887 ) $ (5,425 )

Long-Term Debt (Tables)

Long-Term Debt (Tables)	9 Months Ended
	Sep. 30, 2015
Debt Disclosure [Abstract]
Schedule of Carrying Amounts and Estimated Fair Values of Long-Term Debt	Since Centuri’s debt is not publicly traded, fair values for the secured revolving credit and term loan facility and other debt obligations were based on a conventional discounted cash flow methodology and utilized current market pricing yield curves, across Centuri’s debt maturity spectrum, of other industrial bonds with an assumed credit rating comparable to the Company’s. September 30, 2015 December 31, 2014 Carrying Market Carrying Market (Thousands of dollars) Debentures: Notes, 4.45%, due 2020 $ 125,000 $ 132,769 $ 125,000 $ 133,403 Notes, 6.1%, due 2041 125,000 147,451 125,000 157,290 Notes, 3.875%, due 2022 250,000 263,023 250,000 262,030 Notes, 4.875%, due 2043 250,000 266,370 250,000 280,903 8% Series, due 2026 75,000 99,380 75,000 102,296 Medium-term notes, 7.59% series, due 2017 25,000 26,662 25,000 27,573 Medium-term notes, 7.78% series, due 2022 25,000 30,621 25,000 31,144 Medium-term notes, 7.92% series, due 2027 25,000 32,726 25,000 33,695 Medium-term notes, 6.76% series, due 2027 7,500 8,917 7,500 9,156 Unamortized discount (4,957 ) (5,223 ) 902,543 902,277 Revolving credit facility and commercial paper 97,000 97,000 150,000 150,000 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: 5.25% 2003 Series D, due 2038 — — 20,000 20,277 5.00% 2004 Series B, due 2033 — — 31,200 31,223 4.85% 2005 Series A, due 2035 100,000 100,415 100,000 100,071 4.75% 2006 Series A, due 2036 24,855 25,089 24,855 25,399 Unamortized discount (1,539 ) (1,943 ) 323,316 374,112 Centuri secured revolving credit and term loan facility 208,787 209,213 199,267 200,341 Centuri other debt obligations 28,583 28,868 31,128 31,127 1,560,229 1,656,784 Less: current maturities (19,865 ) (19,192 ) Long-term debt, less current maturities $ 1,540,364 $ 1,637,592

Equity, Other Comprehensive I22

Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income (Tables)	9 Months Ended
	Sep. 30, 2015
Equity [Abstract]
Detailed Activities of Equity and Redeemable Noncontrolling Interest	The table below provides details of activity in equity and the redeemable noncontrolling interest during the nine months ended September 30, 2015. Southwest Gas Corporation Equity Additional Paid-in Capital Accumulated Comprehensive Income (Loss) Redeemable Interest (Temporary Common Stock Retained Non-controlling (In thousands except per share amounts) Shares Amount Total DECEMBER 31, 2014 46,523 $ 48,153 $ 851,381 $ (50,175 ) $ 639,164 $ (2,257 ) $ 1,486,266 $ 20,042 Common stock issuances 852 852 37,467 38,319 Net income (loss) 72,198 80 72,278 454 Redemption value adjustments 5,777 961 6,738 (6,738 ) Foreign currency exchange translation adj. (1,518 ) (1,518 ) (55 ) Other comprehensive income (loss): Net actuarial gain (loss) arising during period, less amortization of unamortized benefit plan cost, net of tax 2,124 2,124 Amounts reclassified to net income, net of tax (FSIRS) 1,556 1,556 Dividends declared Common: $1.215 per share (57,831 ) (57,831 ) SEPTEMBER 30, 2015 47,375 $ 49,005 $ 894,625 $ (48,013 ) $ 654,492 $ (2,177 ) $ 1,547,932 $ 13,703
Related Tax Effects Allocated to Each Component of Other Comprehensive Income (Loss)	Related Tax Effects Allocated to Each Component of Other Comprehensive Income (Loss) (Thousands of dollars) Three Months Ended September 30, 2015 Three Months Ended September 30, 2014 Before- Tax Net-of- Before- Tax Net-of- Defined benefit pension plans: Amortization of prior service cost $ 334 $ (127 ) $ 207 $ 89 $ (34 ) $ 55 Amortization of net actuarial (gain)/loss 8,595 (3,266 ) 5,329 5,914 (2,247 ) 3,667 Regulatory adjustment (7,787 ) 2,959 (4,828 ) (5,178 ) 1,968 (3,210 ) Pension plans other comprehensive income (loss) 1,142 (434 ) 708 825 (313 ) 512 FSIRS (designated hedging activities): Amounts reclassified into net income 836 (317 ) 519 836 (318 ) 518 FSIRS other comprehensive income 836 (317 ) 519 836 (318 ) 518 Foreign currency translation adjustments: Translation adjustments (510 ) — (510 ) — — — Foreign currency other comprehensive income (loss) (510 ) — (510 ) — — — Total other comprehensive income (loss) $ 1,468 $ (751 ) $ 717 $ 1,661 $ (631 ) $ 1,030 Nine Months Ended September 30, 2015 Nine Months Ended September 30, 2014 Before- Tax Tax Net-of- Tax Before- Tax Tax Net-of- Defined benefit pension plans: Amortization of prior service cost $ 1,001 $ (380 ) $ 621 $ 266 $ (101 ) $ 165 Amortization of net actuarial (gain)/loss 25,786 (9,799 ) 15,987 17,742 (6,742 ) $ 11,000 Regulatory adjustment (23,361 ) 8,877 (14,484 ) (15,533 ) 5,903 (9,630 ) Pension plans other comprehensive income (loss) 3,426 (1,302 ) 2,124 2,475 (940 ) 1,535 FSIRS (designated hedging activities): Amounts reclassifed into net income 2,508 (952 ) 1,556 2,509 (954 ) 1,555 FSIRS other comprehensive income 2,508 (952 ) 1,556 2,509 (954 ) 1,555 Foreign currency translation adjustments: Translation adjustments (1,573 ) — (1,573 ) — — — Foreign currency other comprehensive income (loss) (1,573 ) — (1,573 ) — — — Total other comprehensive income (loss) $ 4,361 $ (2,254 ) $ 2,107 $ 4,984 $ (1,894 ) $ 3,090 Twelve Months Ended September 30, 2015 Twelve Months Ended September 30, 2014 Before- Tax Tax Net-of- Tax Before- Tax Tax Net-of- Defined benefit pension plans: Net actuarial gain (loss) $ (173,646 ) $ 65,985 $ (107,661 ) $ 100,345 $ (38,131 ) $ 62,214 Amortization of prior service cost 1,090 (414 ) 676 355 (134 ) 221 Amortization of net actuarial (gain)/loss 31,700 (12,046 ) 19,654 26,285 (9,988 ) 16,297 Prior service cost (6,661 ) 2,531 (4,130 ) — — — Regulatory adjustment 132,480 (50,343 ) 82,137 (116,412 ) 44,236 (72,176 ) Pension plans other comprehensive income (loss) (15,037 ) 5,713 (9,324 ) 10,573 (4,017 ) 6,556 FSIRS (designated hedging activities): Amounts reclassified into net income 3,344 (1,270 ) 2,074 3,345 (1,271 ) 2,074 FSIRS other comprehensive income (loss) 3,344 (1,270 ) 2,074 3,345 (1,271 ) 2,074 Foreign currency translation adjustments: Translation adjustments (2,232 ) — (2,232 ) — — — Foreign currency other comprehensive income (loss) (2,232 ) — (2,232 ) — — — Total other comprehensive income (loss) $ (13,925 ) $ 4,443 $ (9,482 ) $ 13,918 $ (5,288 ) $ 8,630 (1) Tax amounts are calculated using a 38% rate. The Company has elected to indefinitely reinvest the earnings of Centuri’s Canadian subsidiaries in Canada, thus preventing deferred taxes on such earnings. As a result of this assertion, the Company is not recognizing any tax effect or presenting a tax expense or benefit for the currency translation adjustment amount reported in Other Comprehensive Income, as repatriation of earnings is not anticipated.
Rollforward of Accumulated Other Comprehensive Income	The following table represents a rollforward of AOCI, presented on the Company’s Condensed Consolidated Balance Sheets: AOCI—Rollforward (Thousands of dollars) Defined Benefit Plans FSIRS Foreign Currency Items Before-Tax Tax After-Tax Before-Tax Tax After-Tax Before-Tax Tax After-Tax AOCI Beginning Balance AOCI December 31, 2014 $ (57,211 ) $ 21,740 $ (35,471 ) $ (22,688 ) $ 8,621 $ (14,067 ) $ (637 ) $ — $ (637 ) $ (50,175 ) Translation adjustments — — — — — — (1,573 ) — (1,573 ) (1,573 ) Other comprehensive income before reclassifications — — — — — — (1,573 ) — (1,573 ) (1,573 ) FSIRS amounts reclassified from AOCI (1) — — — 2,508 (952 ) 1,556 — — — 1,556 Amortization of prior service cost (2) 1,001 (380 ) 621 — — — — — — 621 Amortization of net actuarial loss (2) 25,786 (9,799 ) 15,987 — — — — — — 15,987 Regulatory adjustment (3) (23,361 ) 8,877 (14,484 ) — — — — — — (14,484 ) Net current period other comprehensive income (loss) 3,426 (1,302 ) 2,124 2,508 (952 ) 1,556 (1,573 ) — (1,573 ) 2,107 Less: Translation adjustment attributable to redeemable noncontrolling interest — — — — — — (55 ) — (55 ) (55 ) Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation 3,426 (1,302 ) 2,124 2,508 (952 ) 1,556 (1,518 ) — (1,518 ) 2,162 Ending Balance AOCI September 30, 2015 $ (53,785 ) $ 20,438 $ (33,347 ) $ (20,180 ) $ 7,669 $ (12,511 ) $ (2,155 ) $ — $ (2,155 ) $ (48,013 ) (1) The FSIRS reclassification amounts are included in the Net interest deductions line item on the Condensed Consolidated Statements of Income. (2) These AOCI components are included in the computation of net periodic benefit cost (see Note 2 – Components of Net Periodic Benefit Cost (3) The regulatory adjustment represents the portion of the activity above that is expected to be recovered through rates in the future (the related regulatory asset is included in the Deferred charges and other assets line item on the Condensed Consolidated Balance Sheets).
Amount Recognized Before Income Tax Associated with Defined Benefit Plans in Accumulated Other Comprehensive Income	The following table represents amounts (before income tax impacts) associated with defined benefit plans, and included in AOCI (in the table above), that have not yet been recognized in net periodic benefit cost: Amounts Recognized in AOCI (Before Tax) (Thousands of dollars) September December Net actuarial (loss) gain $ (413,345 ) $ (439,131 ) Prior service cost (7,372 ) (8,373 ) Less: amount recognized in regulatory assets 366,932 390,293 Recognized in AOCI $ (53,785 ) $ (57,211 )

Construction Services Redeema23

Construction Services Redeemable Noncontrolling Interest (Tables)	9 Months Ended
	Sep. 30, 2015
Noncontrolling Interest [Abstract]
Summary of Redeemable Noncontrolling Interest	The following depicts impacts to the balance of the redeemable noncontrolling interest between the indicated periods. Redeemable (Thousands of dollars): Balance, December 31, 2014 $ 20,042 Net income attributable to redeemable noncontrolling interest 454 Foreign currency exchange translation adjustment (55 ) Adjustment to redemption value (6,738 ) Balance, September 30, 2015 $ 13,703

Nature of Operations and Basi24

Nature of Operations and Basis of Presentation - Additional Information (Detail)	6 Months Ended	9 Months Ended
	Sep. 30, 2015USD ($)	Sep. 30, 2015USD ($)Segment	Sep. 30, 2014USD ($)	Dec. 31, 2014USD ($)
Significant Accounting Policies [Line Items]
Number of segments | Segment		2
Non-cash construction advances - non-cash investing item		$ 2,800,000	$ 7,000,000
Goodwill impairment charges		0
Acquisition date adjustments to goodwill	$ 0	1,380,000
Brigadier Pipelines Inc. [Member]
Significant Accounting Policies [Line Items]
Goodwill assigned for deductible tax purpose	4,900,000	$ 4,900,000
Centuri Construction Group Inc [Member]
Significant Accounting Policies [Line Items]
Ownership percentage in subsidiary		96.60%
Centuri Construction Group Inc [Member] | W.S. Nicholls Western Construction LTD. [Member]
Significant Accounting Policies [Line Items]
Subsidiaries holding interest percentage		50.00%
Pooled funds and mutual funds [Member] | Level 2 - Significant other observable inputs [Member]
Significant Accounting Policies [Line Items]
Money market fund investments	250,000	$ 250,000		$ 250,000
Gas Pipe Materials and Supplies [Member]
Significant Accounting Policies [Line Items]
Gas pipe materials and supplies	$ 25,000,000	$ 25,000,000		$ 23,000,000

Nature of Operations and Basi25

Nature of Operations and Basis of Presentation - Schedule of Goodwill (Detail) - USD ($)	6 Months Ended	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2015
Goodwill [Line Items]
Goodwill, Beginning balance		$ 143,160,000
Acquisition date adjustment	$ 0	1,380,000
Foreign currency translation adjustment		(14,656,000)
Goodwill, Ending balance	129,884,000	129,884,000
Natural Gas Operations [Member]
Goodwill [Line Items]
Goodwill, Beginning balance		10,095,000
Acquisition date adjustment		0
Foreign currency translation adjustment		0
Goodwill, Ending balance	10,095,000	10,095,000
Construction Services [Member]
Goodwill [Line Items]
Goodwill, Beginning balance		133,065,000
Acquisition date adjustment		1,380,000
Foreign currency translation adjustment		(14,656,000)
Goodwill, Ending balance	$ 119,789,000	$ 119,789,000

Nature of Operations and Basi26

Nature of Operations and Basis of Presentation - Intercompany Transactions (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Centuri Construction Group Inc [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Centuri accounts receivable for services provided to Southwest	$ 15,972	$ 9,169

Nature of Operations and Basi27

Nature of Operations and Basis of Presentation - Schedule of Other Property and Investments (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Investment [Line Items]
Net cash surrender value of COLI policies	$ 97,000	$ 99,000
Other property	12,000	10,000
Total	319,243	326,743
Centuri Construction Group Inc [Member]
Investment [Line Items]
Centuri property and equipment	419,000	405,000
Centuri accumulated provision for depreciation and amortization	$ (209,000)	$ (187,000)

Nature of Operations and Basi28

Nature of Operations and Basis of Presentation - Other Income (Deductions) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Other Income and Expenses [Abstract]
Change in COLI policies	$ (3,900)	$ (300)	$ (2,600)	$ 2,900	$ (200)	$ 7,200
Interest income	624	772	1,375	1,881	2,096	1,920
Foreign transaction gain (loss)	(302)	0	(874)	0	(1,052)	0
Miscellaneous income and (expense)	(82)	(32)	873	134	122	(94)
Total other income (deductions)	$ (3,660)	$ 440	$ (1,226)	$ 4,915	$ 966	$ 9,026

Components of Net Periodic Be29

Components of Net Periodic Benefit Cost - Schedule of Components of Net Periodic Benefit Costs (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Qualified Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 6,281	$ 5,340	$ 18,842	$ 16,020	$ 24,182	$ 21,784
Interest cost	11,057	10,860	33,172	32,581	44,031	41,983
Expected return on plan assets	(14,452)	(13,336)	(43,356)	(40,007)	(56,691)	(52,467)
Amortization of net actuarial loss	8,186	5,718	24,557	17,154	30,276	25,219
Net periodic benefit cost	11,072	8,582	33,215	25,748	41,798	36,519
SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	80	73	240	219	313	312
Interest cost	424	436	1,271	1,308	1,708	1,692
Amortization of net actuarial loss	323	196	970	588	1,165	830
Net periodic benefit cost	827	705	2,481	2,115	3,186	2,834
PBOP [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	410	275	1,231	826	1,506	1,131
Interest cost	750	707	2,249	2,122	2,956	2,743
Expected return on plan assets	(866)	(816)	(2,598)	(2,448)	(3,414)	(3,154)
Amortization of prior service costs	334	89	1,001	266	1,090	355
Amortization of net actuarial loss	86	0	259	0	259	236
Net periodic benefit cost	$ 714	$ 255	$ 2,142	$ 766	$ 2,397	$ 1,311

Segment Information - Schedule

Segment Information - Schedule of Segment Reporting Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Segment Reporting Information [Line Items]
Total operating revenues	$ 505,396	$ 432,475	$ 1,778,220	$ 1,494,024	$ 2,405,903	$ 2,032,381
Segment net income (loss)	(4,734)	1,970	72,198	82,380	130,944	139,683
Revenues from external customers [Member]
Segment Reporting Information [Line Items]
Revenues	474,508	409,317	1,704,467	1,422,408	2,311,578	1,934,037
Intersegment revenues [Member]
Segment Reporting Information [Line Items]
Revenues	30,888	23,158	73,753	71,616	94,325	98,344
Natural Gas Operations [Member]
Segment Reporting Information [Line Items]
Total operating revenues	219,420	226,027	1,059,178	983,999	1,457,266	1,356,653
Segment net income (loss)	(18,939)	(11,452)	59,325	62,945	113,252	117,797
Natural Gas Operations [Member] | Revenues from external customers [Member]
Segment Reporting Information [Line Items]
Revenues	219,420	226,027	1,059,178	983,999	1,457,266	1,356,653
Natural Gas Operations [Member] | Intersegment revenues [Member]
Segment Reporting Information [Line Items]
Revenues	0	0	0	0	0	0
Construction Services [Member]
Segment Reporting Information [Line Items]
Total operating revenues	285,976	206,448	719,042	510,025	948,637	675,728
Segment net income (loss)	14,205	13,422	12,873	19,435	17,692	21,886
Construction Services [Member] | Revenues from external customers [Member]
Segment Reporting Information [Line Items]
Revenues	255,088	183,290	645,289	438,409	854,312	577,384
Construction Services [Member] | Intersegment revenues [Member]
Segment Reporting Information [Line Items]
Revenues	$ 30,888	$ 23,158	$ 73,753	$ 71,616	$ 94,325	$ 98,344

Derivatives and Fair Value Me31

Derivatives and Fair Value Measurements - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Derivative [Line Items]
Gains (losses) recognized in income or other comprehensive income for derivative designated cash flow hedges	$ 519,000	$ 518,000	$ 1,556,000	$ 1,555,000	$ 2,074,000	$ 2,074,000
Derivative instrument loss at settlement amortization period			10 years
Cash flow hedging [Member]
Derivative [Line Items]
Gains (losses) recognized in income or other comprehensive income for derivative designated cash flow hedges			$ 0
Minimum [Member]
Derivative [Line Items]
Maturities of natural gas swaps			Oct. 31, 2015
Maximum [Member]
Derivative [Line Items]
Maturities of natural gas swaps			Mar. 31, 2017
Arizona [Member]
Derivative [Line Items]
Natural gas portfolios, maximum % rate			25.00%
California [Member]
Derivative [Line Items]
Natural gas portfolios, maximum % rate			25.00%

Derivatives and Fair Value Me32

Derivatives and Fair Value Measurements - Notional Amounts under Swaps Contracts (Detail) - MMBTU	Sep. 30, 2015	Dec. 31, 2014
Offsetting [Abstract]
Contract notional amounts	8,192,000	5,105,000

Derivatives and Fair Value Me33

Derivatives and Fair Value Measurements - Amount of Gain or Losses Recognized in Income on Derivatives (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain or (loss) recognized in income on derivative	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0
Cash flow hedging [Member] | Net cost of gas sold [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain or (loss) recognized in income on derivative	(3,282)	(2,277)	(4,689)	3,630	(10,682)	7,552
Regulatory deferral accounting treatment [Member] | Cash flow hedging [Member] | Net cost of gas sold [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain or (loss) recognized in income on derivative	$ 3,282	$ 2,277	$ 4,689	$ (3,630)	$ 10,682	$ (7,552)

Derivatives and Fair Value Me34

Derivatives and Fair Value Measurements - Fair Values of Swaps in Condensed Consolidated Balance Sheets (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Asset derivatives not designated as hedging instruments	$ 0	$ 0
Liability derivatives not designated as hedging instruments	(4,887)	(5,425)
Net total not designated as hedging instruments	(4,887)	(5,425)
Swaps [Member] | Other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Asset derivatives not designated as hedging instruments	0	0
Liability derivatives not designated as hedging instruments	(3,425)	(5,062)
Net total not designated as hedging instruments	(3,425)	(5,062)
Swaps [Member] | Other deferred credits [Member]
Derivatives, Fair Value [Line Items]
Asset derivatives not designated as hedging instruments	0	0
Liability derivatives not designated as hedging instruments	(1,462)	(363)
Net total not designated as hedging instruments	$ (1,462)	$ (363)

Derivatives and Fair Value Me35

Derivatives and Fair Value Measurements - Paid to and Received from Counterparties for Settlements of Matured Swaps (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2015	Sep. 30, 2015
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Paid to counterparties	$ 568	$ 5,228	$ 5,971
Received from counterparties	$ 0	$ 0	$ 120

Derivatives and Fair Value Me36

Derivatives and Fair Value Measurements - Regulatory Assets/Liabilities Offsetting Derivatives at Fair Value in Condensed Consolidated Balance Sheets (Detail) - Swaps [Member] - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Prepaids and other current assets [Member]
Derivatives, Fair Value [Line Items]
Net Total	$ 3,425	$ 5,062
Deferred charges and other assets [Member]
Derivatives, Fair Value [Line Items]
Net Total	$ 1,462	$ 363

Derivatives and Fair Value Me37

Derivatives and Fair Value Measurements - Significant Other Observable Inputs (Detail) - Level 2 - Significant other observable inputs [Member] - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Net Assets (Liabilities)	$ (4,887)	$ (5,425)
Swaps [Member] | Other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liabilities	(3,425)	(5,062)
Swaps [Member] | Other deferred credits [Member]
Derivatives, Fair Value [Line Items]
Derivative Liabilities	$ (1,462)	$ (363)

Common Stock - Additional Infor

Common Stock - Additional Information (Detail) - USD ($)	Mar. 10, 2015	Sep. 30, 2015	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Net proceeds to Company			$ 35,419,000	$ 419,000	$ 35,405,000	$ 608,000
Common stock issued through Stock Incentive Plan, Restricted Stock/Unit Plan, and Management Incentive Plan			207,000
BNY Mellon Capital Markets, LLC [Member]
Common stock sold through agent		272,716	645,225
Common stock weighted average price		$ 54.12
Net proceeds to Company		$ 14,610,439	$ 35,167,584
Agent commissions		147,579	355,228
Common stock available for sale under the program		$ 64,477,188	$ 64,477,188		$ 64,477,188
Maximum [Member]
Value of common stock	$ 100,000,000

Long-Term Debt - Schedule of Ca

Long-Term Debt - Schedule of Carrying Amounts and Estimated Fair Values of Long-Term Debt (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Long-term Debt, Current and Noncurrent Abstract
Less: current maturities	$ (19,865)	$ (19,192)
Long-term debt, less current maturities	1,540,364	1,637,592
Carrying Amount [Member]
Debt Instrument [Line Items]
Total long-term debt	1,560,229	1,656,784
Long-term Debt, Current and Noncurrent Abstract
Less: current maturities	(19,865)	(19,192)
Long-term debt, less current maturities	1,540,364	1,637,592
Total long-term debt	1,560,229	1,656,784
Carrying Amount [Member] | IDRBs [Member]
Debt Instrument [Line Items]
Unsecured debt	323,316	374,112
Carrying Amount [Member] | Centuri secured revolving credit and term loan facility [Member]
Debt Instrument [Line Items]
Centuri secured revolving credit and term loan facility	208,787	199,267
Carrying Amount [Member] | Centuri other debt obligations [Member]
Debt Instrument [Line Items]
Centuri other debt obligations	28,583	31,128
Carrying Amount [Member] | Debentures [Member]
Debt Instrument [Line Items]
Unamortized discount	(4,957)	(5,223)
Notes payable	902,543	902,277
Carrying Amount [Member] | Debentures [Member] | Notes, 4.45%, due 2020 [Member]
Debt Instrument [Line Items]
Notes payable	125,000	125,000
Carrying Amount [Member] | Debentures [Member] | Notes, 6.1%, due 2041 [Member]
Debt Instrument [Line Items]
Notes payable	125,000	125,000
Carrying Amount [Member] | Debentures [Member] | Notes, 3.875%, due 2022 [Member]
Debt Instrument [Line Items]
Notes payable	250,000	250,000
Carrying Amount [Member] | Debentures [Member] | Notes, 4.875%, due 2043 [Member]
Debt Instrument [Line Items]
Notes payable	250,000	250,000
Carrying Amount [Member] | Debentures [Member] | 8% Series, due 2026 [Member]
Debt Instrument [Line Items]
Notes payable	75,000	75,000
Carrying Amount [Member] | Debentures [Member] | Medium-term notes, 7.59% series, due 2017 [Member]
Debt Instrument [Line Items]
Notes payable	25,000	25,000
Carrying Amount [Member] | Debentures [Member] | Medium-term notes, 7.78% series, due 2022 [Member]
Debt Instrument [Line Items]
Notes payable	25,000	25,000
Carrying Amount [Member] | Debentures [Member] | Medium-term notes, 7.92% series, due 2027 [Member]
Debt Instrument [Line Items]
Notes payable	25,000	25,000
Carrying Amount [Member] | Debentures [Member] | Medium-term notes, 6.76% series, due 2027 [Member]
Debt Instrument [Line Items]
Notes payable	7,500	7,500
Carrying Amount [Member] | Debentures [Member] | Revolving credit facility and commercial paper [Member]
Debt Instrument [Line Items]
Line of credit facility	97,000	150,000
Carrying Amount [Member] | Variable-rate bonds [Member] | Tax-exempt Series A, due 2028 [Member]
Debt Instrument [Line Items]
Unsecured debt	50,000	50,000
Carrying Amount [Member] | Variable-rate bonds [Member] | 2003 Series A, due 2038 [Member]
Debt Instrument [Line Items]
Unsecured debt	50,000	50,000
Carrying Amount [Member] | Variable-rate bonds [Member] | 2008 Series A, due 2038 [Member]
Debt Instrument [Line Items]
Unsecured debt	50,000	50,000
Carrying Amount [Member] | Variable-rate bonds [Member] | 2009 Series A, due 2039 [Member]
Debt Instrument [Line Items]
Unsecured debt	50,000	50,000
Carrying Amount [Member] | Fixed-rate bonds [Member]
Debt Instrument [Line Items]
Unamortized discount	(1,539)	(1,943)
Carrying Amount [Member] | Fixed-rate bonds [Member] | 5.25% 2003 Series D, due 2038 [Member]
Debt Instrument [Line Items]
Unsecured debt		20,000
Carrying Amount [Member] | Fixed-rate bonds [Member] | 5.00% 2004 Series B, due 2033 [Member]
Debt Instrument [Line Items]
Unsecured debt		31,200
Carrying Amount [Member] | Fixed-rate bonds [Member] | 4.85% 2005 Series A, due 2035 [Member]
Debt Instrument [Line Items]
Unsecured debt	100,000	100,000
Carrying Amount [Member] | Fixed-rate bonds [Member] | 4.75% 2006 Series A, due 2036 [Member]
Debt Instrument [Line Items]
Unsecured debt	24,855	24,855
Market Value [Member] | Centuri secured revolving credit and term loan facility [Member]
Debt Instrument [Line Items]
Centuri secured revolving credit and term loan facility	209,213	200,341
Market Value [Member] | Centuri other debt obligations [Member]
Debt Instrument [Line Items]
Centuri other debt obligations	28,868	31,127
Market Value [Member] | Debentures [Member] | Notes, 4.45%, due 2020 [Member]
Debt Instrument [Line Items]
Notes payable, fair value disclosure	132,769	133,403
Market Value [Member] | Debentures [Member] | Notes, 6.1%, due 2041 [Member]
Debt Instrument [Line Items]
Notes payable, fair value disclosure	147,451	157,290
Market Value [Member] | Debentures [Member] | Notes, 3.875%, due 2022 [Member]
Debt Instrument [Line Items]
Notes payable, fair value disclosure	263,023	262,030
Market Value [Member] | Debentures [Member] | Notes, 4.875%, due 2043 [Member]
Debt Instrument [Line Items]
Notes payable, fair value disclosure	266,370	280,903
Market Value [Member] | Debentures [Member] | 8% Series, due 2026 [Member]
Debt Instrument [Line Items]
Notes payable, fair value disclosure	99,380	102,296
Market Value [Member] | Debentures [Member] | Medium-term notes, 7.59% series, due 2017 [Member]
Debt Instrument [Line Items]
Notes payable, fair value disclosure	26,662	27,573
Market Value [Member] | Debentures [Member] | Medium-term notes, 7.78% series, due 2022 [Member]
Debt Instrument [Line Items]
Notes payable, fair value disclosure	30,621	31,144
Market Value [Member] | Debentures [Member] | Medium-term notes, 7.92% series, due 2027 [Member]
Debt Instrument [Line Items]
Notes payable, fair value disclosure	32,726	33,695
Market Value [Member] | Debentures [Member] | Medium-term notes, 6.76% series, due 2027 [Member]
Debt Instrument [Line Items]
Notes payable, fair value disclosure	8,917	9,156
Market Value [Member] | Debentures [Member] | Revolving credit facility and commercial paper [Member]
Debt Instrument [Line Items]
Line of credit facility, fair value	97,000	150,000
Market Value [Member] | Variable-rate bonds [Member] | Tax-exempt Series A, due 2028 [Member]
Debt Instrument [Line Items]
Line of credit facility, fair value	50,000	50,000
Market Value [Member] | Variable-rate bonds [Member] | 2003 Series A, due 2038 [Member]
Debt Instrument [Line Items]
Line of credit facility, fair value	50,000	50,000
Market Value [Member] | Variable-rate bonds [Member] | 2008 Series A, due 2038 [Member]
Debt Instrument [Line Items]
Line of credit facility, fair value	50,000	50,000
Market Value [Member] | Variable-rate bonds [Member] | 2009 Series A, due 2039 [Member]
Debt Instrument [Line Items]
Line of credit facility, fair value	50,000	50,000
Market Value [Member] | Fixed-rate bonds [Member] | 5.25% 2003 Series D, due 2038 [Member]
Debt Instrument [Line Items]
Line of credit facility, fair value	0	20,277
Market Value [Member] | Fixed-rate bonds [Member] | 5.00% 2004 Series B, due 2033 [Member]
Debt Instrument [Line Items]
Line of credit facility, fair value	0	31,223
Market Value [Member] | Fixed-rate bonds [Member] | 4.85% 2005 Series A, due 2035 [Member]
Debt Instrument [Line Items]
Line of credit facility, fair value	100,415	100,071
Market Value [Member] | Fixed-rate bonds [Member] | 4.75% 2006 Series A, due 2036 [Member]
Debt Instrument [Line Items]
Line of credit facility, fair value	$ 25,089	$ 25,399

Long-Term Debt - Schedule of 40

Long-Term Debt - Schedule of Carrying Amounts and Estimated Fair Values of Long-Term Debt (Parenthetical) (Detail)	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014	May. 31, 2015
5.25% 2003 Series D, due 2038 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	5.25%
Debt instrument due date	Dec. 1, 2038
5.00% 2004 Series B, due 2033 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate			5.00%
Debt instrument due date	Dec. 1, 2033
Debentures [Member] | Notes, 4.45%, due 2020 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	4.45%	4.45%
Debt instrument due date	Dec. 1, 2020	Dec. 1, 2020
Debentures [Member] | Notes, 6.1%, due 2041 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	6.10%	6.10%
Debt instrument due date	Feb. 15, 2041	Feb. 15, 2041
Debentures [Member] | Notes, 3.875%, due 2022 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	3.875%	3.875%
Debt instrument due date	Apr. 1, 2022	Apr. 1, 2022
Debentures [Member] | Notes, 4.875%, due 2043 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	4.875%	4.875%
Debt instrument due date	Oct. 1, 2043	Oct. 1, 2043
Debentures [Member] | 8% Series, due 2026 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	8.00%	8.00%
Debt instrument due date	Aug. 1, 2026	Aug. 1, 2026
Debentures [Member] | Medium-term notes, 7.59% series, due 2017 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	7.59%	7.59%
Debt instrument due date	Jan. 17, 2017	Jan. 17, 2017
Debentures [Member] | Medium-term notes, 7.78% series, due 2022 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	7.78%	7.78%
Debt instrument due date	Feb. 3, 2022	Feb. 3, 2022
Debentures [Member] | Medium-term notes, 7.92% series, due 2027 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	7.92%	7.92%
Debt instrument due date	Jun. 4, 2027	Jun. 4, 2027
Debentures [Member] | Medium-term notes, 6.76% series, due 2027 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	6.76%	6.76%
Debt instrument due date	Sep. 24, 2027	Sep. 24, 2027
Variable-rate bonds [Member] | Tax-exempt Series A, due 2028 [Member]
Debt Instrument [Line Items]
Debt instrument due date	Dec. 1, 2028	Dec. 1, 2028
Variable-rate bonds [Member] | 2003 Series A, due 2038 [Member]
Debt Instrument [Line Items]
Debt instrument due date	Mar. 1, 2038	Mar. 1, 2038
Variable-rate bonds [Member] | 2008 Series A, due 2038 [Member]
Debt Instrument [Line Items]
Debt instrument due date	Mar. 1, 2038	Mar. 1, 2038
Variable-rate bonds [Member] | 2009 Series A, due 2039 [Member]
Debt Instrument [Line Items]
Debt instrument due date	Dec. 1, 2039	Dec. 1, 2039
Fixed-rate bonds [Member] | 5.25% 2003 Series D, due 2038 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	5.25%	5.25%
Debt instrument due date	Mar. 1, 2038	Mar. 1, 2038
Fixed-rate bonds [Member] | 5.00% 2004 Series B, due 2033 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	5.00%	5.00%
Debt instrument due date	Dec. 1, 2033	Dec. 1, 2033
Fixed-rate bonds [Member] | 4.85% 2005 Series A, due 2035 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	4.85%	4.85%
Debt instrument due date	Oct. 1, 2035	Oct. 1, 2035
Fixed-rate bonds [Member] | 4.75% 2006 Series A, due 2036 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	4.75%	4.75%
Debt instrument due date	Sep. 1, 2036	Sep. 1, 2036

Long-Term Debt - Additional Inf

Long-Term Debt - Additional Information (Detail) - USD ($)	1 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	May. 31, 2015	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Debt Instrument [Line Items]
Redemption of long term debt			$ 143,325,000	$ 21,528,000	$ 260,952,000	$ 28,272,000
Southwest Gas Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility maximum borrowing capacity	$ 300,000,000		300,000,000		300,000,000
Line of credit designated as long term debt	150,000,000		150,000,000		150,000,000
Line of credit designated for working capital purposes	150,000,000		$ 150,000,000		150,000,000
Credit facility expiration date			Mar. 1, 2020
Borrowings outstanding under facility	47,000,000		$ 47,000,000		47,000,000
Southwest Gas Credit Facility [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Applicable margin			1.00%
Southwest Gas Credit Facility [Member] | Alternative base rate [Member]
Debt Instrument [Line Items]
Applicable margin			0.00%
Southwest Gas Credit Facility [Member] | Before Amendment [Member]
Debt Instrument [Line Items]
Credit facility expiration date			Mar. 1, 2019
Centuri Construction Group Inc [Member] | Secured Revolving Credit and Term Loan Facility [Member]
Debt Instrument [Line Items]
Credit facility maximum borrowing capacity	300,000,000		$ 300,000,000		300,000,000
Credit facility expiration date			Oct. 31, 2019
Borrowings outstanding under facility	209,000,000		$ 209,000,000		209,000,000
Debt secured by assets	557,000,000		$ 557,000,000		557,000,000
5.00% 2004 Series B, due 2033 [Member]
Debt Instrument [Line Items]
Redemption of long term debt		$ 31,200,000
Debt instrument interest rate		5.00%
Debt instrument original due date			Dec. 1, 2033
Commercial Paper Program [Member]
Debt Instrument [Line Items]
Borrowings outstanding under facility	50,000,000		$ 50,000,000		$ 50,000,000
5.25% 2003 Series D, due 2038 [Member]
Debt Instrument [Line Items]
Redemption of long term debt	$ 20,000,000
Debt instrument interest rate	5.25%		5.25%		5.25%
Debt instrument original due date			Dec. 1, 2038

Equity, Other Comprehensive I42

Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income - Detailed Activities of Equity and Redeemable Noncontrolling Interest (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Schedule Of Stockholders Equity [Line Items]
Balance			$ 1,486,266
Balance			$ 20,042
Balance, shares			46,523,184
Common stock issuances			$ 38,319
Net income (loss)	$ (4,734)	$ 1,970	72,198	$ 82,380	$ 130,944	$ 139,683
Net income (loss)			72,278
Redemption value adjustments			6,738
Balance	13,703		13,703		13,703
Foreign currency exchange translation adj.			(1,518)
Other comprehensive income (loss):
Net actuarial gain (loss) arising during period, less amortization of unamortized benefit plan cost, net of tax	708	512	2,124	1,535	(9,324)	6,556
Amounts reclassified into net income	519	$ 518	1,556	$ 1,555	2,074	$ 2,074
Dividends declared Common: $1.215 per share			(57,831)
Balance	$ 1,547,932		$ 1,547,932		$ 1,547,932
Balance, shares	47,375,398		47,375,398		47,375,398
Common Stock [Member]
Schedule Of Stockholders Equity [Line Items]
Balance			$ 48,153
Balance, shares			46,523,000
Common stock issuances			$ 852
Common stock issuance, shares			852,000
Other comprehensive income (loss):
Balance	$ 49,005		$ 49,005		$ 49,005
Balance, shares	47,375,000		47,375,000		47,375,000
Additional Paid-in Capital [Member]
Schedule Of Stockholders Equity [Line Items]
Balance			$ 851,381
Common stock issuances			37,467
Redemption value adjustments			5,777
Other comprehensive income (loss):
Balance	$ 894,625		894,625		$ 894,625
Accumulated Other Comprehensive Income (Loss) [Member]
Schedule Of Stockholders Equity [Line Items]
Balance			(50,175)
Foreign currency exchange translation adj.			(1,518)
Other comprehensive income (loss):
Net actuarial gain (loss) arising during period, less amortization of unamortized benefit plan cost, net of tax			2,124
Amounts reclassified into net income			1,556
Balance	(48,013)		(48,013)		(48,013)
Retained Earnings [Member]
Schedule Of Stockholders Equity [Line Items]
Balance			639,164
Net income (loss)			72,198
Redemption value adjustments			961
Other comprehensive income (loss):
Dividends declared Common: $1.215 per share			(57,831)
Balance	654,492		654,492		654,492
Non-controlling Interest [Member]
Schedule Of Stockholders Equity [Line Items]
Balance			(2,257)
Net income (loss)			80
Other comprehensive income (loss):
Balance	(2,177)		(2,177)		(2,177)
Redeemable Noncontrolling Interest (Temporary Equity) [Member]
Schedule Of Stockholders Equity [Line Items]
Balance			20,042
Net income (loss)			454
Redemption value adjustments			(6,738)
Foreign currency exchange translation adj.			(55)
Balance	$ 13,703		$ 13,703		$ 13,703

Equity, Other Comprehensive I43

Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income - Detailed Activities of Equity and Redeemable Noncontrolling Interest (Parenthetical) (Detail) - $ / shares	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Statement of Stockholders' Equity [Abstract]
Dividends declared Common, per share	$ 0.405	$ 0.365	$ 1.215	$ 1.095	$ 1.580	$ 1.425

Equity, Other Comprehensive I44

Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income - Related Tax Effects Allocated to Each Component of Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Equity [Abstract]
Net actuarial gain/(loss), Before-Tax Amount					$ (173,646)	$ 100,345
Amortization of prior service cost, Before-Tax Amount	$ 334	$ 89	$ 1,001	$ 266	1,090	355
Amortization of net actuarial (gain)/loss, Before-Tax Amount	8,595	5,914	25,786	17,742	31,700	26,285
Prior service cost, Before-Tax Amount					(6,661)	0
Regulatory adjustment, Before-Tax Amount	(7,787)	(5,178)	(23,361)	(15,533)	132,480	(116,412)
Net current period other comprehensive income (loss), Defined Benefit Plans Before-Tax	1,142	825	3,426	2,475	(15,037)	10,573
Amounts reclassified into net income, Before-Tax Amount	836	836	2,508	2,509	3,344	3,345
FSIRS other comprehensive income (loss), Before-Tax Amount	836	836	2,508	2,509	3,344	3,345
Translation adjustments, Before-Tax Amount	(510)	0	(1,573)	0	(2,232)	0
Foreign currency other comprehensive income (loss), Before-Tax Amount	(510)	0	(1,573)	0	(2,232)	0
Total other comprehensive income (loss), Before-Tax Amount	1,468	1,661	4,361	4,984	(13,925)	13,918
Net actuarial gain/(loss), Tax (Expense) or Benefit					65,985	(38,131)
Amortization of prior service cost, Tax (Expense) or Benefit	(127)	(34)	(380)	(101)	(414)	(134)
Amortization of net actuarial (gain)/loss, Tax (Expense) or Benefit	(3,266)	(2,247)	(9,799)	(6,742)	(12,046)	(9,988)
Prior service cost, Tax (Expense) or Benefit					2,531	0
Regulatory adjustment, Tax (Expense) or Benefit	2,959	1,968	8,877	5,903	(50,343)	44,236
Pension plans other comprehensive income (loss), Tax (Expense) or Benefit	(434)	(313)	(1,302)	(940)	5,713	(4,017)
Amounts reclassified into net income, Tax (Expense) or Benefit	(317)	(318)	(952)	(954)	(1,270)	(1,271)
FSIRS other comprehensive income (loss), Tax (Expense) or Benefit	(317)	(318)	(952)	(954)	(1,270)	(1,271)
Translation adjustments, Tax (Expense) or Benefit	0	0	0	0	0	0
Foreign currency other comprehensive income (loss), Tax (Expense) or Benefit	0	0	0	0	0	0
Total other comprehensive income (loss), Tax (Expense) or Benefit	(751)	(631)	(2,254)	(1,894)	4,443	(5,288)
Net actuarial gain/(loss), Net-of-Tax Amount	0	0	0	0	(107,661)	62,214
Amortization of prior service cost, Net-of-Tax Amount	207	55	621	165	676	221
Amortization of net actuarial (gain)/loss, Defined Benefit Plans After-Tax	5,329	3,667	15,987	11,000	19,654	16,297
Prior service cost, Net-of-Tax Amount	0	0	0	0	(4,130)	0
Regulatory adjustment, Net-of-Tax Amount	(4,828)	(3,210)	(14,484)	(9,630)	82,137	(72,176)
Pension plans other comprehensive income (loss), Net-of-Tax Amount	708	512	2,124	1,535	(9,324)	6,556
Amounts reclassified into net income	519	518	1,556	1,555	2,074	2,074
FSIRS other comprehensive income (loss), Net-of-Tax Amount	519	518	1,556	1,555	2,074	2,074
Translation adjustments, Net-of-Tax Amount	(510)	0	(1,573)	0	(2,232)	0
Foreign currency other comprehensive income (loss), Net-of-Tax Amount	(510)	0	(1,573)	0	(2,232)	0
Total other comprehensive income (loss), net of tax	$ 717	$ 1,030	$ 2,107	$ 3,090	$ (9,482)	$ 8,630

Equity, Other Comprehensive I45

Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income - Related Tax Effects Allocated to Each Component of Other Comprehensive Income (Loss) (Parenthetical) (Detail)	9 Months Ended
	Sep. 30, 2015USD ($)
Equity [Abstract]
Other comprehensive income loss, effective income tax rate	38.00%
Tax expense or benefit for currency translation adjustment	$ 0

Equity, Other Comprehensive I46

Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income - Additional Information (Detail) $ in Millions	Sep. 30, 2015USD ($)
Equity [Abstract]
Amount of FSIRS existing AOCI losses expected to reclassified income in next twelve months	$ 2.1

Equity, Other Comprehensive I47

Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income - Rollforward of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Equity [Abstract]
Beginning Balance AOCI December 31, 2014, Defined Benefit Plans Before-Tax			$ (57,211)
Translation adjustments, Defined Benefit Plans Before-Tax			0
Other comprehensive income before reclassifications, Defined Benefit Plans Before-Tax			0
Amortization of prior service cost, Defined Benefit Plans Before-Tax	$ 334	$ 89	1,001	$ 266	$ 1,090	$ 355
Amortization of net actuarial loss, Defined Benefit Plans Before-Tax	8,595	5,914	25,786	17,742	31,700	26,285
Regulatory adjustment, Defined Benefit Plans Before-Tax	(7,787)	(5,178)	(23,361)	(15,533)	132,480	(116,412)
Net current period other comprehensive income (loss), Defined Benefit Plans Before-Tax	1,142	825	3,426	2,475	(15,037)	10,573
Less: Translation adjustment attributable to redeemable noncontrolling interest, Defined Benefit Plans Before-Tax			0
Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation, Defined Benefit Plans Before-Tax			3,426
Ending Balance AOCI September 30, 2015, Defined Benefit Plans Before-Tax	(53,785)		(53,785)		(53,785)
Beginning Balance AOCI December 31, 2014, Defined Benefit Plans Tax (Expense) Benefit			21,740
Translation adjustments, Defined Benefit Plans Tax (Expense) Benefit			0
Other comprehensive income before reclassifications, Defined Benefit Plans Tax (Expense) Benefit			0
Amortization of prior service cost, Defined Benefit Plans Tax (Expense) Benefit	(127)	(34)	(380)	(101)	(414)	(134)
Amortization of net actuarial loss, Defined Benefit Plans Tax (Expense) Benefit	(3,266)	(2,247)	(9,799)	(6,742)	(12,046)	(9,988)
Regulatory adjustment, Defined Benefit Plans Tax (Expense) Benefit	2,959	1,968	8,877	5,903	(50,343)	44,236
Pension plans other comprehensive income (loss), Tax (Expense) or Benefit	(434)	(313)	(1,302)	(940)	5,713	(4,017)
Less: Translation adjustment attributable to redeemable noncontrolling interest, Defined Benefit Plans Tax (Expense) Benefit			0
Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation, Defined Benefit Plans Tax (Expense) Benefit			(1,302)
Ending Balance AOCI September 30, 2015, Defined Benefit Plans Tax (Expense) Benefit	20,438		20,438		20,438
Beginning Balance AOCI December 31, 2014, Defined Benefit Plans After-Tax			(35,471)
Translation adjustments, Defined Benefit Plans After-Tax			0
Other comprehensive income before reclassifications, Defined Benefit Plans After-Tax			0
Amortization of prior service cost, Defined Benefit Plans After-Tax	207	55	621	165	676	221
Amortization of net actuarial (gain)/loss, Defined Benefit Plans After-Tax	5,329	3,667	15,987	11,000	19,654	16,297
Regulatory adjustment, Defined Benefit Plans After-Tax			(14,484)
Net defined benefit pension plans	708	512	2,124	1,535	(9,324)	6,556
Less: Translation adjustment attributable to redeemable noncontrolling interest, Defined Benefit Plans After-Tax			0
Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation, Defined Benefit Plans After-Tax			2,124
Ending Balance AOCI September 30, 2015, Defined Benefit Plans After-Tax	(33,347)		(33,347)		(33,347)
Beginning Balance AOCI December 31, 2014, FSIRS - Before-Tax			(22,688)
Translation adjustments, FSIRS - Before-Tax			0
Other comprehensive income before reclassifications, FSIRS - Before-Tax			0
FSIRS amounts reclassified from AOCI, FSIRS - Before-Tax	836	836	2,508	2,509	3,344	3,345
Net current period other comprehensive income (loss), FSIRS - Before-Tax	836	836	2,508	2,509	3,344	3,345
Less: Translation adjustment attributable to redeemable noncontrolling interest, FSIRS - Before-Tax			0
Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation, FSIRS - Before-Tax			2,508
Ending Balance AOCI September 30, 2015, FSIRS - Before-Tax	(20,180)		(20,180)		(20,180)
Beginning Balance AOCI December 31, 2014, FSIRS - Tax (Expense) Benefit			8,621
Translation adjustments, FSIRS - Tax (Expense) Benefit			0
Other comprehensive income before reclassifications, FSIRS - Tax (Expense) Benefit			0
FSIRS amounts reclassified from AOCI, FSIRS - Tax (Expense) Benefit	(317)	(318)	(952)	(954)	(1,270)	(1,271)
Net current period other comprehensive income (loss), FSIRS - Tax (Expense) Benefit	(317)	(318)	(952)	(954)	(1,270)	(1,271)
Less: Translation adjustment attributable to redeemable noncontrolling interest, FSIRS - Tax (Expense) Benefit			0
Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation, FSIRS - Tax (Expense) Benefit			(952)
Ending Balance AOCI September 30, 2015, FSIRS - Tax (Expense) Benefit	7,669		7,669		7,669
Beginning Balance AOCI December 31, 2014, FSIRS - After-Tax			(14,067)
Translation adjustments, FSIRS - After-Tax			0
Other comprehensive income before reclassifications, FSIRS - After-Tax			0
FSIRS amounts reclassified from AOCI, FSIRS - After-Tax	519	518	1,556	1,555	2,074	2,074
Net forward-starting interest rate swaps	519	518	1,556	1,555	2,074	2,074
Less: Translation adjustment attributable to redeemable noncontrolling interest, FSIRS - After-Tax			0
Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation, FSIRS - After-Tax			1,556
Ending Balance AOCI September 30, 2015, FSIRS - After-Tax	(12,511)		(12,511)		(12,511)
Beginning Balance AOCI December 31, 2014, Foreign Currency Items Before-Tax			(637)
Translation adjustments, Foreign Currency Items Before-Tax	(510)	0	(1,573)	0	(2,232)	0
Other comprehensive income before reclassifications, Foreign Currency Items Before-Tax	(510)	0	(1,573)	0	(2,232)	0
FSIRS amounts reclassified from AOCI, Foreign Currency Items Before-Tax			0
Amortization of prior service cost, Foreign Currency Items Before-Tax			0
Amortization of net actuarial loss, Foreign Currency Items Before-Tax			0
Regulatory adjustment, Foreign Currency Items Before-Tax			0
Net current period other comprehensive income (loss), Foreign Currency Items Before-Tax			(1,573)
Less: Translation adjustment attributable to redeemable noncontrolling interest, Foreign Currency Items Before-Tax			(55)
Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation, Foreign Currency Items Before-Tax			(1,518)
Ending Balance AOCI September 30, 2015, Foreign Currency Items Before-Tax	(2,155)		(2,155)		(2,155)
Beginning Balance AOCI December 31, 2014, Foreign Currency items - Tax (Expense) Benefit			0
Translation adjustments, Foreign Currency items - Tax (Expense) Benefit	0	0	0	0	0	0
Other comprehensive income before reclassifications, Foreign Currency items - Tax (Expense) Benefit			0
FSIRS amounts reclassified from AOCI, Foreign Currency items - Tax (Expense) Benefit			0
Amortization of prior service cost ,Foreign Currency items - Tax (Expense) Benefit			0
Amortization of net actuarial loss, Foreign Currency items - Tax (Expense) Benefit			0
Regulatory adjustment, Foreign Currency items - Tax (Expense) Benefit			0
Net current period other comprehensive income (loss), Foreign Currency items - Tax (Expense) Benefit			0
Less: Translation adjustment attributable to redeemable noncontrolling interest, Foreign Currency items - Tax (Expense) Benefit			0
Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation, Foreign Currency items - Tax (Expense) Benefit	0	0	0	0	0	0
Ending Balance AOCI September 30, 2015, Foreign Currency items - Tax (Expense) Benefit	0		0		0
Beginning Balance AOCI December 31, 2014, Foreign Currency items - After-Tax			(637)
Translation adjustments, Foreign Currency items - After-Tax	(510)	0	(1,573)	0	(2,232)	0
Other comprehensive income before reclassifications, Foreign Currency items - After-Tax	(510)	0	(1,573)	0	(2,232)	0
FSIRS amounts reclassified from AOCI, Foreign Currency items - After-Tax			0
Amortization of prior service cost, Foreign Currency items - After-Tax			0
Amortization of net actuarial loss, Foreign Currency items - After-Tax			0
Regulatory adjustment, Foreign Currency items - After-Tax			0
Net current period other comprehensive income (loss), Foreign Currency items - After-Tax			(1,573)
Less: Translation adjustment attributable to redeemable noncontrolling interest, Foreign Currency items - After-Tax			(55)
Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation, Foreign Currency Items - After-Tax			(1,518)
Ending Balance AOCI September 30, 2015, Foreign Currency items - After-Tax	(2,155)		(2,155)		(2,155)
Beginning Balance AOCI December 31, 2014, AOCI			(50,175)
Translation adjustments, AOCI	(1,573)		(1,573)		(1,573)
Other comprehensive income before reclassifications, AOCI			(1,573)
Amounts reclassified into net income	519	518	1,556	1,555	2,074	2,074
Amortization of prior service cost, AOCI	207	55	621	165	676	221
Amortization of net actuarial loss	5,329	3,667	15,987	11,000	19,654	16,297
Regulatory adjustment, AOCI			(14,484)
Total other comprehensive income (loss), net of tax	717	$ 1,030	2,107	$ 3,090	(9,482)	$ 8,630
Less: Translation adjustment attributable to redeemable noncontrolling interest, AOCI	(55)		(55)		(55)
Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation, AOCI	2,162		2,162		2,162
Ending Balance AOCI September 30, 2015, AOCI	$ (48,013)		$ (48,013)		$ (48,013)

Equity, Other Comprehensive I48

Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income - Amount Recognized Before Income Tax Associated with Defined Benefit Plans in Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Recognized in AOCI	$ 53,785	$ 57,211
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net actuarial (loss) gain	(413,345)	(439,131)
Prior service cost	(7,372)	(8,373)
Less: amount recognized in regulatory assets	366,932	390,293
Recognized in AOCI	$ (53,785)	$ (57,211)

Acquisition of Construction S49

Acquisition of Construction Services Businesses - Additional Information (Detail) - USD ($)	6 Months Ended	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2015
Business Combinations [Abstract]
Acquisition date adjustment	$ 0	$ 1,380,000

Construction Services Redeema50

Construction Services Redeemable Noncontrolling Interests - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	9 Months Ended
	Oct. 31, 2014	Sep. 30, 2015
Additional Paid-in Capital [Member]
Noncontrolling Interest [Line Items]
Adjustment to redemption value		$ 5,777
Principal Previous Owners [Member] | Link-Line and WS Nicholls [Member]
Noncontrolling Interest [Line Items]
Equity interest percentage	10.00%
Description of equity interest		The agreement, associated with that approximate 10% equity interest, provided special dividend rights which entitled the sellers, as holders, to dividends equal to 3.4% of dividends paid at the level of Centuri, and subject to certain conditions, such interests could become exchangeable for a 3.4% equity interest in Centuri. In consideration of the underlying exchange rights of the original agreement, earnings attribution by Centuri to the previous owners has also occurred in an amount equivalent to 3.4% of Centuri earnings since October 2014. During the third quarter of 2015, the sellers formally exercised their exchange rights under the terms of that original agreement. No new rights were conveyed to the noncontrolling parties as a result of the exchange and no new consideration was involved. The ability of the sellers to redeem their holdings for cash at specified dates remains intact. The previous owners may exit their investment retained by requiring the purchase of a portion of their interest commencing July 2017 and in incremental amounts each anniversary date thereafter. The shares subject to the election cumulate (if earlier elections are not made) such that 100% of their interest retained is subject to the election beginning in July 2022.
Equity interest dividend rights, percentage of dividends paid by Centuri	3.40%
First redemption date to exchange holdings for cash		2017-07
Principal Previous Owners [Member] | Link-Line and WS Nicholls [Member] | Construction Services [Member]
Noncontrolling Interest [Line Items]
Equity interest exchangeable percentage in Centuri	3.40%
Percentage of earnings attribution by Centuri to previous owners	3.40%
Principal Previous Owners [Member] | Link-Line and WS Nicholls [Member] | Construction Services [Member] | Maximum [Member]
Noncontrolling Interest [Line Items]
Percentage of retained interest may elect to sell to centuri		100.00%

Construction Services Redeema51

Construction Services Redeemable Noncontrolling Interests - Summary of Redeemable Noncontrolling Interest (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2015USD ($)
Redeemable Noncontrolling Interest [Line Items]
Balance	$ 20,042
Adjustment to redemption value	6,738
Balance	13,703
Redeemable Noncontrolling Interest (Temporary Equity) [Member]
Redeemable Noncontrolling Interest [Line Items]
Balance	20,042
Net income attributable to redeemable noncontrolling interest	454
Foreign currency exchange translation adjustment	(55)
Adjustment to redemption value	(6,738)
Balance	$ 13,703