Leases - Schedule of Rental and Lease Payments (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Lessee, Lease, Description [Line Items]
Rental payments/lease expense	$ 64,047	$ 67,236
Southwest Gas Corporation
Lessee, Lease, Description [Line Items]
Rental payments/lease expense	4,556	4,926
Centuri
Lessee, Lease, Description [Line Items]
Rental payments/lease expense	$ 59,491	$ 62,310

Rental expense for the reporting period incurred under operating leases, including minimum and any contingent rent expense, net of related sublease income.

Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=77902758&loc=d3e41499-112717

Name:	us-gaap_OperatingLeasesRentExpenseNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration