Other Comprehensive Income and Accumulated Other Comprehensive Income - AOCI Rollforward (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, attributable to parent	$ 3,310,036
Other comprehensive income (loss), before tax	(2,313)	$ 355
Other comprehensive income (loss), tax	(122)	(62)
Total other comprehensive income (loss), net of tax	(2,435)	$ 293
Ending balance, attributable to parent	$ 3,356,241
Statutory income tax rate	24.00%	24.00%
Southwest Gas Corporation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, attributable to parent	$ 3,183,615
Other comprehensive income (loss), before tax	506	$ 258
Other comprehensive income (loss), tax	(122)	(62)
Total other comprehensive income (loss), net of tax	384	196
Ending balance	3,277,539	2,666,130
Ending balance, attributable to parent	3,277,539
Defined Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, before tax	(53,352)
Beginning balance, tax (expense) benefit	12,804
Beginning balance	(40,548)
Other comprehensive income (loss), before tax	506
Other comprehensive income (loss), tax	(122)
Total other comprehensive income (loss), net of tax	384
Ending balance, before tax	(52,846)
Ending balance, tax (expense) benefit	12,682
Ending balance	(40,164)
Defined Benefit Plans | Southwest Gas Corporation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, attributable to parent, before tax	(53,352)
Beginning balance, attributable to parent, tax (expense) benefit	12,804
Beginning balance, attributable to parent	(40,548)
Other comprehensive income (loss), before tax	506
Other comprehensive income (loss), tax	(122)
Total other comprehensive income (loss), net of tax	384
Ending balance, attributable to parent, before tax	(52,846)
Ending balance, attributable to parent, tax (expense) benefit	12,682
Ending balance, attributable to parent	(40,164)
Amortization of prior service cost
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income (loss), before tax	44
Other comprehensive income (loss), tax	(11)
Total other comprehensive income (loss), net of tax	33
Amortization of prior service cost | Southwest Gas Corporation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification from AOCI, before Tax	44	44
Reclassification from AOCI, tax	(11)	(11)
Reclassification from AOCI, net of tax	33	33
Amortization of net actuarial loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income (loss), before tax	1,910
Other comprehensive income (loss), tax	(459)
Total other comprehensive income (loss), net of tax	1,451
Amortization of net actuarial loss | Southwest Gas Corporation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification from AOCI, before Tax	1,910	333
Reclassification from AOCI, tax	(459)	(80)
Reclassification from AOCI, net of tax	1,451	253
Regulatory adjustment | Southwest Gas Corporation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income (loss), before tax	(1,448)
Other comprehensive income (loss), tax	348
Total other comprehensive income (loss), net of tax	(1,100)
Foreign Currency Items
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, before tax	(3,239)
Beginning balance, tax (expense) benefit	0
Beginning balance	(3,239)
Other comprehensive income (loss) before reclassifications, before tax	(2,819)
Other comprehensive income (loss) before reclassifications, tax	0
Other comprehensive income (loss) before reclassifications, net of tax	(2,819)
Ending balance, before tax	(6,058)
Ending balance, tax (expense) benefit	0
Ending balance	(6,058)
AOCI Including Portion Attributable to Noncontrolling Interest
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income (loss) before reclassifications, net of tax	(2,435)
AOCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(43,787)	(44,242)
Ending balance	(46,222)	(43,949)
AOCI | Southwest Gas Corporation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(40,548)	(38,261)
Ending balance	$ (40,164)	$ (38,065)