CONDENSED CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Operating revenues:
Gas operating revenues	$ 210,834	$ 209,980	$ 976,095	$ 989,368	$ 1,355,666	$ 1,359,581
Utility infrastructure services revenues	203,082	200,256	966,941	1,005,844	1,346,391	1,374,724
Total operating revenues	791,226	725,230	2,384,793	2,271,780	3,232,930	3,058,434
Operating expenses:
Net cost of gas sold	36,321	35,068	264,615	292,854	356,925	393,141
Operations and maintenance	101,764	109,652	304,964	321,190	407,924	414,289
Depreciation and amortization	80,139	75,370	245,009	223,251	324,995	286,522
Taxes other than income taxes	15,787	15,308	47,507	46,640	63,195	61,579
Utility infrastructure services expenses	502,951	451,574	1,252,489	1,154,238	1,671,478	1,534,442
Total operating expenses	736,962	686,972	2,114,584	2,038,173	2,824,517	2,689,973
Operating income (loss)	54,264	38,258	270,209	233,607	408,413	368,461
Other income and (expenses):
Net interest deductions	(28,311)	(27,434)	(83,141)	(80,662)	(111,705)	(106,502)
Other income (deductions)	1,799	(1,158)	(11,046)	6,827	(7,788)	(4,448)
Total other income and (expenses)	(26,512)	(28,592)	(94,187)	(73,835)	(119,493)	(110,950)
Income (loss) before income taxes	27,752	9,666	176,022	159,772	288,920	257,511
Income tax expense (benefit)	6,689	3,141	42,073	35,031	63,065	63,294
Net income (loss)	21,063	6,525	133,949	124,741	225,855	194,217
Net income attributable to noncontrolling interest	2,790	1,172	5,169	2,523	5,357	2,695
Net income attributable to Southwest Gas Holdings, Inc.	$ 18,273	$ 5,353	$ 128,780	$ 122,218	$ 220,498	$ 191,522
Earnings per share:
Basic (in USD per share)	$ 0.32	$ 0.10	$ 2.31	$ 2.26	$ 3.97	$ 3.60
Diluted (in USD per share)	$ 0.32	$ 0.10	$ 2.31	$ 2.26	$ 3.97	$ 3.59
Weighted average shares:
Basic (in shares)	56,271	54,670	55,683	53,996	55,508	53,219
Diluted (in shares)	56,357	54,748	55,753	54,063	55,577	53,287
Southwest Gas Corporation
Operating revenues:
Gas operating revenues	$ 210,834	$ 209,980	$ 976,095	$ 989,368	$ 1,355,666	$ 1,359,581
Operating expenses:
Net cost of gas sold	36,321	35,068	264,615	292,854	356,925	393,141
Operations and maintenance	101,159	109,039	303,567	319,572	406,169	412,330
Depreciation and amortization	55,942	52,372	173,865	159,327	230,158	205,594
Taxes other than income taxes	15,787	15,308	47,507	46,640	63,195	61,579
Total operating expenses	209,209	211,787	789,554	818,393	1,056,447	1,072,644
Operating income (loss)	1,625	(1,807)	186,541	170,975	299,219	286,937
Other income and (expenses):
Net interest deductions	(26,103)	(23,619)	(75,152)	(70,063)	(100,115)	(92,000)
Other income (deductions)	1,751	(1,353)	(10,947)	6,185	(7,615)	(5,194)
Total other income and (expenses)	(24,352)	(24,972)	(86,099)	(63,878)	(107,730)	(97,194)
Income (loss) before income taxes	(22,727)	(26,779)	100,442	107,097	191,489	189,743
Income tax expense (benefit)	(6,754)	(6,767)	20,874	20,351	35,496	43,456
Net income (loss)	(15,973)	(20,012)	79,568	86,746	155,993	146,287
Net income attributable to Southwest Gas Holdings, Inc.	(15,973)	(20,012)			155,993	146,287
Centuri
Operating revenues:
Utility infrastructure services revenues	$ 580,392	$ 515,250	$ 1,408,698	$ 1,282,412	$ 1,877,264	$ 1,698,853