CONDENSED CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Operating revenues:
Gas operating revenues	$ 209,980	$ 217,523	$ 989,368	$ 987,515	$ 1,359,581	$ 1,354,000
Utility infrastructure services revenues	515,250	450,623	1,282,412	1,105,844	1,698,853	1,479,792
Total operating revenues	725,230	668,146	2,271,780	2,093,359	3,058,434	2,833,792
Operating expenses:
Net cost of gas sold	35,068	49,903	292,854	319,101	393,141	412,307
Operations and maintenance	109,652	105,508	321,190	313,294	414,289	406,137
Depreciation and amortization	75,370	62,156	223,251	185,941	286,522	247,803
Taxes other than income taxes	15,308	15,036	46,640	44,959	61,579	59,580
Utility infrastructure services expenses	451,574	395,862	1,154,238	1,007,485	1,534,442	1,349,862
Total operating expenses	686,972	628,465	2,038,173	1,870,780	2,689,973	2,475,689
Operating income (loss)	38,258	39,681	233,607	222,579	368,461	358,103
Other income and (expenses):
Net interest deductions	(27,434)	(24,548)	(80,662)	(70,831)	(106,502)	(92,032)
Other income (deductions)	(1,158)	889	6,827	(6,151)	(4,448)	(6,401)
Total other income and (expenses)	(28,592)	(23,659)	(73,835)	(76,982)	(110,950)	(98,433)
Income (loss) before income taxes	9,666	16,022	159,772	145,597	257,511	259,670
Income tax expense (benefit)	3,141	3,691	35,031	33,421	63,294	51,098
Net income	6,525	12,331	124,741	112,176	194,217	208,572
Net income (loss) attributable to noncontrolling interests	1,172	0	2,523	(797)	2,695	(866)
Net income attributable to Southwest Gas Holdings, Inc.	$ 5,353	$ 12,331	$ 122,218	$ 112,973	$ 191,522	$ 209,438
Basic earnings per share (in USD per share)	$ 0.10	$ 0.25	$ 2.26	$ 2.31	$ 3.60	$ 4.30
Diluted earnings per share (in USD per share)	$ 0.10	$ 0.25	$ 2.26	$ 2.31	$ 3.59	$ 4.29
Average number of common shares (in shares)	54,670	49,493	53,996	48,916	53,219	48,728
Average shares (assuming dilution) (in shares)	54,748	49,553	54,063	48,968	53,287	48,781
Southwest Gas Corporation
Operating revenues:
Gas operating revenues	$ 209,980	$ 217,523	$ 989,368	$ 987,515	$ 1,359,581	$ 1,354,000
Operating expenses:
Net cost of gas sold	35,068	49,903	292,854	319,101	393,141	412,307
Operations and maintenance	109,039	104,657	319,572	312,055	412,330	404,549
Depreciation and amortization	52,372	47,924	159,327	145,549	205,594	193,828
Taxes other than income taxes	15,308	15,036	46,640	44,959	61,579	59,580
Total operating expenses	211,787	217,520	818,393	821,664	1,072,644	1,070,264
Operating income (loss)	(1,807)	3	170,975	165,851	286,937	283,736
Other income and (expenses):
Net interest deductions	(23,619)	(20,399)	(70,063)	(59,803)	(92,000)	(77,914)
Other income (deductions)	(1,353)	836	6,185	(5,861)	(5,194)	(6,425)
Total other income and (expenses)	(24,972)	(19,563)	(63,878)	(65,664)	(97,194)	(84,339)
Income (loss) before income taxes	(26,779)	(19,560)	107,097	100,187	189,743	199,397
Income tax expense (benefit)	(6,767)	(5,890)	20,351	20,886	43,456	45,714
Net income	(20,012)	(13,670)	86,746	79,301	146,287	153,683
Net income attributable to Southwest Gas Holdings, Inc.	$ (20,012)	$ (13,670)	$ 86,746	$ 79,301	$ 146,287	$ 153,683