Income Taxes - Summary of Income Before Taxes for Continuing and Discontinued Operations (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Southwest Gas Corporation
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total income before income taxes	$ 216,473	$ 194,873	$ 198,144

Amount, before tax, of income (loss) including portion attributable to noncontrolling interest. Includes, but is not limited to, income (loss) from continuing operations, discontinued operations and equity method investments.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=124431353&loc=SL124452729-227067

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.18)
-URI http://asc.fasb.org/extlink&oid=123367319&loc=SL114868664-224227

Name:	us-gaap_IncomeLossIncludingPortionAttributableToNoncontrollingInterest
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration