CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Net income	$ (9,294)	$ 21,063	$ 136,025	$ 133,949	$ 241,061	$ 225,855
Defined benefit pension plans:
Net actuarial loss	0	0	0	0	(43,730)	(54,026)
Amortization of prior service cost	183	220	547	659	766	901
Amortization of net actuarial loss	8,474	7,187	25,420	21,563	32,608	26,004
Prior service cost	0	0	0	0	0	(1,426)
Regulatory adjustment	(7,277)	(6,380)	(21,831)	(19,140)	2,959	21,130
Net defined benefit pension plans	1,380	1,027	4,136	3,082	(7,397)	(7,417)
Forward-starting interest rate swaps (“FSIRS”):
Amounts reclassified into net income (loss)	413	783	1,240	2,054	1,653	2,689
Net forward-starting interest rate swaps	413	783	1,240	2,054	1,653	2,689
Foreign currency translation adjustments	(2,056)	1,024	(324)	(1,187)	2,576	(280)
Total other comprehensive income (loss), net of tax	(263)	2,834	5,052	3,949	(3,168)	(5,008)
Comprehensive income (loss)	(9,557)	23,897	141,077	137,898	237,893	220,847
Comprehensive income attributable to noncontrolling interest	2,282	2,790	5,189	5,169	6,681	5,357
Comprehensive income (loss) attributable to Southwest Gas Holdings, Inc.	(11,839)	21,107	135,888	132,729	231,212	215,490
Southwest Gas Corporation
Net income	(27,544)	(15,973)	102,584	79,568	182,134	155,993
Defined benefit pension plans:
Net actuarial loss	0	0	0	0	(43,730)	(54,026)
Amortization of prior service cost	183	220	547	659	766	901
Amortization of net actuarial loss	8,474	7,187	25,420	21,563	32,608	26,004
Prior service cost	0	0	0	0	0	(1,426)
Regulatory adjustment	(7,277)	(6,380)	(21,831)	(19,140)	2,959	21,130
Net defined benefit pension plans	1,380	1,027	4,136	3,082	(7,397)	(7,417)
Forward-starting interest rate swaps (“FSIRS”):
Amounts reclassified into net income (loss)	413	783	1,240	2,054	1,653	2,689
Net forward-starting interest rate swaps	413	783	1,240	2,054	1,653	2,689
Total other comprehensive income (loss), net of tax	1,793	1,810	5,376	5,136	(5,744)	(4,728)
Comprehensive income (loss)	$ (25,751)	$ (14,163)	$ 107,960	$ 84,704	$ 176,390	$ 151,265