CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Net income	$ 39,881	$ 22,832	$ 112,886	$ 118,216	$ 211,317	$ 200,023
Defined benefit pension plans:
Net actuarial loss	0	0	0	0	(54,026)	(15,524)
Amortization of prior service cost	220	242	440	483	923	990
Amortization of net actuarial loss	7,187	4,441	14,375	8,883	23,258	21,658
Prior service cost	0	0	0	0	(1,426)	0
Regulatory adjustment	(6,380)	(4,064)	(12,760)	(8,128)	23,445	(2,895)
Net defined benefit pension plans	1,027	619	2,055	1,238	(7,826)	4,229
Forward-starting interest rate swaps (“FSIRS”):
Amounts reclassified into net income	635	636	1,271	1,271	2,541	2,541
Net forward-starting interest rate swaps	635	636	1,271	1,271	2,541	2,541
Foreign currency translation adjustments	1,794	787	(2,211)	1,578	(1,751)	169
Total other comprehensive income (loss), net of tax	3,456	2,042	1,115	4,087	(7,036)	6,939
Comprehensive income	43,337	24,874	114,001	122,303	204,281	206,962
Comprehensive income attributable to noncontrolling interests	1,916	776	2,379	1,351	3,739	1,523
Comprehensive income attributable to Southwest Gas Holdings, Inc.	41,421	24,098	111,622	120,952	200,542	205,439
Southwest Gas Corporation
Net income	11,942	3,369	95,541	106,758	151,954	152,629
Defined benefit pension plans:
Net actuarial loss	0	0	0	0	(54,026)	(15,524)
Amortization of prior service cost	220	242	440	483	923	990
Amortization of net actuarial loss	7,187	4,441	14,375	8,883	23,258	21,658
Prior service cost	0	0	0	0	(1,426)	0
Regulatory adjustment	(6,380)	(4,064)	(12,760)	(8,128)	23,445	(2,895)
Net defined benefit pension plans	1,027	619	2,055	1,238	(7,826)	4,229
Forward-starting interest rate swaps (“FSIRS”):
Amounts reclassified into net income	635	636	1,271	1,271	2,541	2,541
Net forward-starting interest rate swaps	635	636	1,271	1,271	2,541	2,541
Total other comprehensive income (loss), net of tax	1,662	1,255	3,326	2,509	(5,285)	6,770
Comprehensive income	$ 13,604	$ 4,624	$ 98,867	$ 109,267	$ 146,669	$ 159,399