CONDENSED CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Thousands, $ 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
Operating revenues:
Gas operating revenues	$ 255,848	$ 210,834	$ 1,070,576	$ 976,095	$ 1,445,066	$ 1,355,666
Utility infrastructure services revenues	632,848	580,392	1,525,448	1,408,698	2,065,038	1,877,264
Total operating revenues	888,696	791,226	2,596,024	2,384,793	3,510,104	3,232,930
Operating expenses:
Net cost of gas sold	63,710	36,321	296,227	264,615	374,449	356,925
Operations and maintenance	122,927	101,764	334,450	304,964	437,602	407,924
Depreciation and amortization	91,380	80,139	267,670	245,009	354,688	324,995
Taxes other than income taxes	20,109	15,787	60,134	47,507	76,087	63,195
Utility infrastructure services expenses	567,270	502,951	1,381,524	1,252,489	1,858,464	1,671,478
Total operating expenses	865,396	736,962	2,340,005	2,114,584	3,101,290	2,824,517
Operating income (loss)	23,300	54,264	256,019	270,209	408,814	408,413
Other income and (expenses):
Net interest deductions	(31,298)	(28,311)	(81,201)	(83,141)	(109,537)	(111,705)
Other income (deductions)	(3,112)	1,799	(3,975)	(11,046)	282	(7,788)
Total other income and (expenses)	(34,410)	(26,512)	(85,176)	(94,187)	(109,255)	(119,493)
Income (loss) before income taxes	(11,110)	27,752	170,843	176,022	299,559	288,920
Income tax expense (benefit)	(1,816)	6,689	34,818	42,073	58,498	63,065
Net income (loss)	(9,294)	21,063	136,025	133,949	241,061	225,855
Net income attributable to noncontrolling interest	2,282	2,790	5,189	5,169	6,681	5,357
Net income (loss) attributable to Southwest Gas Holdings, Inc.	$ (11,576)	$ 18,273	$ 130,836	$ 128,780	$ 234,380	$ 220,498
Earnings (loss) per share:
Basic (in USD per share)	$ (0.19)	$ 0.32	$ 2.23	$ 2.31	$ 4.03	$ 3.97
Diluted (in USD per share)	$ (0.19)	$ 0.32	$ 2.23	$ 2.31	$ 4.02	$ 3.97
Weighted average shares:
Basic (in shares)	59,688	56,271	58,639	55,683	58,209	55,508
Diluted (in shares)	59,816	56,357	58,742	55,753	58,312	55,577
Southwest Gas Corporation
Operating revenues:
Gas operating revenues	$ 255,848	$ 210,834	$ 1,070,576	$ 976,095	$ 1,445,066	$ 1,355,666
Operating expenses:
Net cost of gas sold	63,710	36,321	296,227	264,615	374,449	356,925
Operations and maintenance	119,708	101,159	328,980	303,567	431,795	406,169
Depreciation and amortization	61,359	55,942	187,688	173,865	249,118	230,158
Taxes other than income taxes	20,109	15,787	60,134	47,507	76,087	63,195
Total operating expenses	264,886	209,209	873,029	789,554	1,131,449	1,056,447
Operating income (loss)	(9,038)	1,625	197,547	186,541	313,617	299,219
Other income and (expenses):
Net interest deductions	(24,922)	(26,103)	(71,263)	(75,152)	(97,259)	(100,115)
Other income (deductions)	(4,287)	1,751	(4,902)	(10,947)	(545)	(7,615)
Total other income and (expenses)	(29,209)	(24,352)	(76,165)	(86,099)	(97,804)	(107,730)
Income (loss) before income taxes	(38,247)	(22,727)	121,382	100,442	215,813	191,489
Income tax expense (benefit)	(10,703)	(6,754)	18,798	20,874	33,679	35,496
Net income (loss)	(27,544)	(15,973)	$ 102,584	$ 79,568	182,134	155,993
Net income (loss) attributable to Southwest Gas Holdings, Inc.	$ (27,544)	$ (15,973)			$ 182,134	$ 155,993