CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ 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
Net income (loss)	$ 6,525	$ 12,331	$ 124,741	$ 112,176	$ 194,217	$ 208,572
Defined benefit pension plans:
Net actuarial gain (loss)	0	0	0	0	(15,524)	(32,701)
Amortization of prior service cost	241	254	724	762	977	969
Amortization of net actuarial loss	4,442	6,387	13,325	19,161	19,713	23,105
Regulatory adjustment	(4,065)	(5,746)	(12,193)	(17,236)	(1,214)	6,021
Net defined benefit pension plans	618	895	1,856	2,687	3,952	(2,606)
Forward-starting interest rate swaps (“FSIRS”):
Amounts reclassified into net income	635	636	1,906	1,907	2,540	2,426
Net forward-starting interest rate swaps	635	636	1,906	1,907	2,540	2,426
Foreign currency translation adjustments	(447)	599	1,131	(1,002)	(877)	(1,092)
Total other comprehensive income (loss), net of tax	806	2,130	4,893	3,592	5,615	(1,272)
Comprehensive income (loss)	7,331	14,461	129,634	115,768	199,832	207,300
Comprehensive income (loss) attributable to noncontrolling interests	1,172	0	2,523	(797)	2,695	(866)
Comprehensive income attributable to Southwest Gas Holdings, Inc.	6,159	14,461	127,111	116,565	197,137	208,166
Southwest Gas Corporation
Net income (loss)	(20,012)	(13,670)	86,746	79,301	146,287	153,683
Defined benefit pension plans:
Net actuarial gain (loss)	0	0	0	0	(15,524)	(32,701)
Amortization of prior service cost	241	254	724	762	977	969
Amortization of net actuarial loss	4,442	6,387	13,325	19,161	19,713	23,105
Regulatory adjustment	(4,065)	(5,746)	(12,193)	(17,236)	(1,214)	6,021
Net defined benefit pension plans	618	895	1,856	2,687	3,952	(2,606)
Forward-starting interest rate swaps (“FSIRS”):
Amounts reclassified into net income	635	636	1,906	1,907	2,540	2,426
Net forward-starting interest rate swaps	635	636	1,906	1,907	2,540	2,426
Total other comprehensive income (loss), net of tax	1,253	1,531	3,762	4,594	6,492	(180)
Comprehensive income (loss)	$ (18,759)	$ (12,139)	$ 90,508	$ 83,895	$ 152,779	$ 153,503