Nature of Operations and Basis of Presentation - Additional Information (Detail) - USD ($)	6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Significant Accounting Policies [Line Items]
Non-cash construction advances - non-cash investing item	$ 1,600,000	$ 2,500,000
Accrued taxes	(6,100,000)	(12,121,000)	$ 32,361,000	$ (28,140,000)
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	$ (2,823,000)	(6,456,000)	23,024,000	(17,334,000)
Accounting Standards Update 2016-09 [Member]
Significant Accounting Policies [Line Items]
Accrued taxes		7,800,000		22,700,000
Accounting Standards Update 2016-09 [Member] | Southwest Gas Corporation [Member]
Significant Accounting Policies [Line Items]
Accrued taxes		4,800,000		11,600,000
Accounting Standards Update 2016-09 [Member] | Scenario, Previously Reported [Member]
Significant Accounting Policies [Line Items]
Accrued taxes		5,800,000		18,900,000
Accounting Standards Update 2016-09 [Member] | Scenario, Previously Reported [Member] | Southwest Gas Corporation [Member]
Significant Accounting Policies [Line Items]
Accrued taxes		$ 2,800,000		$ 7,800,000
Pooled Funds and Mutual Funds [Member] | Level 2 - Significant Other Observable Inputs [Member]
Significant Accounting Policies [Line Items]
Money market fund investments	7,700,000		7,700,000		$ 5,300,000
Gas Pipe Materials and Supplies [Member]
Significant Accounting Policies [Line Items]
Gas pipe materials and operating supplies	$ 39,000,000		$ 39,000,000		$ 30,000,000