Leases - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Jan. 01, 2019
Accounting Standards Update 2016-02
Lessee, Lease, Description [Line Items]
Operating lease ROU assets		$ 58,400
Lease liabilities		60,800
Southwest Gas Corporation
Lessee, Lease, Description [Line Items]
Operating lease ROU assets	$ 1,977
Lease liabilities	$ 1,998
Lease renewal term (up to)	3 years
Southwest Gas Corporation | Accounting Standards Update 2016-02
Lessee, Lease, Description [Line Items]
Operating lease ROU assets		1,900
Lease liabilities		$ 1,900
Centuri
Lessee, Lease, Description [Line Items]
Operating lease ROU assets	$ 57,267
Lease liabilities	$ 59,825
Lease renewal term (up to)	5 years
Lease termination period	1 year
Short-term lease cost	$ 2,575
Minimum | Southwest Gas Corporation
Lessee, Lease, Description [Line Items]
Lease remaining lease term	1 year
Minimum | Centuri
Lessee, Lease, Description [Line Items]
Lease remaining lease term	1 year
Maximum | Southwest Gas Corporation
Lessee, Lease, Description [Line Items]
Lease remaining lease term	10 years
Maximum | Centuri
Lessee, Lease, Description [Line Items]
Lease remaining lease term	14 years