Leases - Components of Lease Expense (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)
Finance lease cost:
Total lease cost	$ 5,828
Southwest Gas Corporation
Lessee, Lease, Description [Line Items]
Operating lease cost	406
Centuri
Lessee, Lease, Description [Line Items]
Operating lease cost	2,805
Finance lease cost:
Amortization of ROU assets	35
Interest on lease liabilities	7
Total finance lease cost	42
Short-term lease cost	$ 2,575