CONDENSED CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Thousands, $ 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
Operating revenues:
Gas operating revenues	$ 262,434	$ 258,711	$ 765,261	$ 779,388	$ 1,354,812	$ 1,367,124
Utility infrastructure services revenues	259,066	253,408	763,859	805,588	1,343,565	1,371,305
Total operating revenues	757,247	713,011	1,593,567	1,546,550	3,166,934	3,001,350
Operating expenses:
Net cost of gas sold	67,473	65,182	228,294	257,786	355,672	407,976
Operations and maintenance	99,419	105,293	203,200	211,538	415,812	410,145
Depreciation and amortization	77,217	70,342	164,870	147,881	320,226	273,308
Taxes other than income taxes	15,342	15,126	31,720	31,332	62,716	61,307
Utility infrastructure services expenses	430,224	402,199	749,538	702,664	1,620,101	1,478,730
Total operating expenses	689,675	658,142	1,377,622	1,351,201	2,774,527	2,631,466
Operating income	67,572	54,869	215,945	195,349	392,407	369,884
Other income and (expenses):
Net interest deductions	(26,450)	(26,831)	(54,830)	(53,228)	(110,828)	(103,616)
Other income (deductions)	7,925	1,146	(12,845)	7,985	(10,745)	(2,401)
Total other income and (expenses)	(18,525)	(25,685)	(67,675)	(45,243)	(121,573)	(106,017)
Income before income taxes	49,047	29,184	148,270	150,106	270,834	263,867
Income tax expense (benefit)	9,166	6,352	35,384	31,890	59,517	63,844
Net income	39,881	22,832	112,886	118,216	211,317	200,023
Net income attributable to noncontrolling interests	1,916	776	2,379	1,351	3,739	1,523
Net income attributable to Southwest Gas Holdings, Inc.	$ 37,965	$ 22,056	$ 110,507	$ 116,865	$ 207,578	$ 198,500
Earnings per share:
Basic (in USD per share)	$ 0.68	$ 0.41	$ 2.00	$ 2.18	$ 3.77	$ 3.82
Diluted (in USD per share)	$ 0.68	$ 0.41	$ 1.99	$ 2.18	$ 3.76	$ 3.82
Weighted average shares:
Basic (in shares)	55,462	53,935	55,386	53,654	55,105	51,914
Diluted (in shares)	55,532	54,003	55,448	53,716	55,171	51,977
Southwest Gas Corporation
Operating revenues:
Gas operating revenues	$ 262,434	$ 258,711	$ 765,261	$ 779,388	$ 1,354,812	$ 1,367,124
Operating expenses:
Net cost of gas sold	67,473	65,182	228,294	257,786	355,672	407,976
Operations and maintenance	99,320	104,991	202,408	210,533	414,049	407,948
Depreciation and amortization	53,198	49,343	117,923	106,955	226,588	201,146
Taxes other than income taxes	15,342	15,126	31,720	31,332	62,716	61,307
Total operating expenses	235,333	234,642	580,345	606,606	1,059,025	1,078,377
Operating income	27,101	24,069	184,916	172,782	295,787	288,747
Other income and (expenses):
Net interest deductions	(23,991)	(23,345)	(49,049)	(46,444)	(97,631)	(88,780)
Other income (deductions)	7,838	1,592	(12,698)	7,538	(10,719)	(3,005)
Total other income and (expenses)	(16,153)	(21,753)	(61,747)	(38,906)	(108,350)	(91,785)
Income before income taxes	10,948	2,316	123,169	133,876	187,437	196,962
Income tax expense (benefit)	(994)	(1,053)	27,628	27,118	35,483	44,333
Net income	11,942	3,369	95,541	106,758	151,954	152,629
Net income attributable to Southwest Gas Holdings, Inc.	11,942	3,369			151,954	152,629
Centuri
Operating revenues:
Utility infrastructure services revenues	$ 494,813	$ 454,300	$ 828,306	$ 767,162	$ 1,812,122	$ 1,634,226