Leases - Additional Information (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Jan. 01, 2019
Southwest Gas Corporation
Lessee, Lease, Description [Line Items]
Operating lease ROU assets	$ 2,008
Lease liabilities	$ 2,035
Lease renewal term (up to)	3 years
Southwest Gas Corporation | Minimum
Lessee, Lease, Description [Line Items]
Lease remaining lease term	1 year
Southwest Gas Corporation | Maximum
Lessee, Lease, Description [Line Items]
Lease remaining lease term	10 years
Centuri
Lessee, Lease, Description [Line Items]
Operating lease ROU assets	$ 71,377
Lease liabilities	$ 73,974
Lease renewal term (up to)	5 years
Lease termination period	1 year
Short-term lease total future lease payments	$ 13,200
Centuri | Maximum
Lessee, Lease, Description [Line Items]
Lease remaining lease term	19 years
Accounting Standards Update 2016-02
Lessee, Lease, Description [Line Items]
Operating lease ROU assets		$ 58,400
Lease liabilities		60,800
Accounting Standards Update 2016-02 | Southwest Gas Corporation
Lessee, Lease, Description [Line Items]
Operating lease ROU assets		1,900
Lease liabilities		$ 1,900