Nature of Operations and Basis of Presentation - Additional Information (Detail) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Significant Accounting Policies [Line Items]
Non-cash construction advances - non-cash investing item	$ 477,000	$ 900,000
Accrued taxes	20,397,000	38,196,000	$ 10,660,000	$ (18,118,000)
Goodwill impairment charges	$ 0
Centuri Construction Group Inc [Member]
Significant Accounting Policies [Line Items]
Ownership percentage in subsidiary	96.60%
Southwest Gas Corporation [Member]
Significant Accounting Policies [Line Items]
Accrued taxes	$ 25,176,000	36,049,000	10,637,000	(18,047,000)
Accounting Standards Update 2016-09 [Member]
Significant Accounting Policies [Line Items]
Accrued taxes		38,196,000		(18,118,000)
Accounting Standards Update 2016-09 [Member] | Southwest Gas Corporation [Member]
Significant Accounting Policies [Line Items]
Accrued taxes		36,049,000		(18,047,000)
Accounting Standards Update 2016-09 [Member] | Scenario, Previously Reported [Member]
Significant Accounting Policies [Line Items]
Accrued taxes		36,300,000		(21,900,000)
Accounting Standards Update 2016-09 [Member] | Scenario, Previously Reported [Member] | Southwest Gas Corporation [Member]
Significant Accounting Policies [Line Items]
Accrued taxes		$ 34,200,000		$ (21,800,000)
Pooled Funds and Mutual Funds [Member] | Level 2 - Significant Other Observable Inputs [Member]
Significant Accounting Policies [Line Items]
Money market fund investments	14,100,000		14,100,000		$ 5,300,000
Gas Pipe Materials and Supplies [Member]
Significant Accounting Policies [Line Items]
Gas pipe materials and operating supplies	$ 35,000,000		$ 35,000,000		$ 30,000,000