CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Statement of Comprehensive Income [Abstract]
Net income	$ 97,250	$ 118,845	$ 185,607	$ 284,825
Defined benefit pension plans:
Net actuarial gain (loss)	0	0	44,974	(43,730)
Amortization of prior service cost	33	182	580	840
Amortization of net actuarial loss	6,616	8,474	32,036	30,037
Regulatory adjustment	(5,523)	(7,277)	(65,273)	4,753
Net defined benefit pension plans	1,126	1,379	12,317	(8,100)
Forward-starting interest rate swaps (“FSIRS”):
Amounts reclassified into net income	416	413	1,655	2,244
Net forward-starting interest rate swaps	416	413	1,655	2,244
Foreign currency translation adjustments	1,247	823	444	6,541
Total other comprehensive income, net of tax	2,789	2,615	14,416	685
Comprehensive income	100,039	121,460	200,023	285,510
Comprehensive income attributable to noncontrolling interests	1,072	1,552	5,943	7,750
Comprehensive income attributable to Southwest Gas Holdings, Inc.	$ 98,967	$ 119,908	$ 194,080	$ 277,760