CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Net income	$ 73,005	$ 95,384	$ 194,268	$ 198,742
Defined benefit pension plans:
Net actuarial loss	0	0	(54,026)	(15,524)
Amortization of prior service cost	220	241	945	1,002
Amortization of net actuarial loss	7,188	4,441	20,513	23,603
Prior service cost	0	0	(1,426)	0
Regulatory adjustment	(6,380)	(4,063)	25,760	(4,574)
Net defined benefit pension plans	1,028	619	(8,234)	4,507
Forward-starting interest rate swaps (“FSIRS”):
Amounts reclassified into net income	636	635	2,542	2,541
Net forward-starting interest rate swaps	636	635	2,542	2,541
Foreign currency translation adjustments	(4,005)	791	(2,758)	(1,308)
Total other comprehensive income (loss), net of tax	(2,341)	2,045	(8,450)	5,740
Comprehensive income	70,664	97,429	185,818	204,482
Comprehensive income attributable to noncontrolling interests	463	575	2,599	747
Comprehensive income attributable to Southwest Gas Holdings, Inc.	70,201	96,854	183,219	203,735
Southwest Gas Corporation
Net income	83,599	103,389	143,381	151,882
Defined benefit pension plans:
Net actuarial loss	0	0	(54,026)	(15,524)
Amortization of prior service cost	220	241	945	1,002
Amortization of net actuarial loss	7,188	4,441	20,513	23,603
Prior service cost	0	0	(1,426)	0
Regulatory adjustment	(6,380)	(4,063)	25,760	(4,574)
Net defined benefit pension plans	1,028	619	(8,234)	4,507
Forward-starting interest rate swaps (“FSIRS”):
Amounts reclassified into net income	636	635	2,542	2,541
Net forward-starting interest rate swaps	636	635	2,542	2,541
Total other comprehensive income (loss), net of tax	1,664	1,254	(5,692)	7,048
Comprehensive income	$ 85,263	$ 104,643	$ 137,689	$ 158,930