Leases - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019	Jan. 01, 2019
Southwest Gas Corporation
Lessee, Lease, Description [Line Items]
Operating lease ROU assets	$ 2,072	$ 2,072
Lease liabilities	$ 2,097	$ 2,097
Lease renewal term (up to)	3 years	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	$ 60,301	$ 60,301
Lease liabilities	$ 63,150	$ 63,150
Lease renewal term (up to)	5 years	5 years
Lease termination period		1 year
Short-term lease cost	$ 3,357	$ 5,932
Centuri | Minimum
Lessee, Lease, Description [Line Items]
Lease remaining lease term		1 year
Centuri | Maximum
Lessee, Lease, Description [Line Items]
Lease remaining lease term		14 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