Background, Organization, and Summary of Significant Accounting Policies - Narrative (Details)	1 Months Ended		3 Months Ended	12 Months Ended
	Jul. 31, 2023	Mar. 31, 2023 USD ($)	Mar. 31, 2023 USD ($)	Dec. 31, 2023 USD ($) $ / shares	Dec. 31, 2022 USD ($) $ / shares	Dec. 31, 2021 USD ($)	Nov. 03, 2023 $ / oneTen-thousandthShare $ / shares shares	May 31, 2023 USD ($)
Significant Accounting Policies [Line Items]
Common stock dividend, number of preferred stock purchase right per share | shares							1
Common stock, par (in USD per share) | $ / shares				$ 1	$ 1		$ 1
Preferred stock purchase right, purchase price per one ten-thousandth of one preferred stock | $ / oneTen-thousandthShare							300.00
Decrease of net cost of gas sold				$ (1,253,269,000)	$ (799,060,000)	$ (430,907,000)
Increase in deferred purchased gas costs				117,770,000	147,215,000	343,728,000
Amortization expenses				26,700,000	29,800,000	17,300,000
Increase (decrease) of capital expenditures incurred but not yet paid				(17,100,000)	23,400,000	15,500,000
Cumulative foreign earnings				$ 94,000,000
Deferred purchased gas costs, recovered or refunded period				1 year
Deferred purchased gas costs				$ 552,885,000	450,120,000
Accrued purchased gas cost				0	207,000,000
Current assets held for sale adjustment				21,377,000	1,737,530,000
Dividends declared but not yet paid				44,400,000	41,600,000
Accrued purchased gas costs				88,000,000	0
Debt portion				6,851,000	3,535,000	1,046,000
Equity AFUDC				1,869,000	0	0
Certain Assets Associated With Previous Corporate Headquarters
Significant Accounting Policies [Line Items]
Other property and investments adjustment		$ 27,000,000	$ 27,000,000
Current assets held for sale adjustment		27,000,000	27,000,000
Estimated loss on disposition of assets				$ 5,200,000
Arizona
Significant Accounting Policies [Line Items]
Gas cost balancing account rate, period	2 years
Deferred purchased gas costs								$ 358,000,000
Gas cost balancing account recovery period				12 months
Money Market Funds
Significant Accounting Policies [Line Items]
Money market fund investments				$ 48,900,000	29,700,000
Customer relationships
Significant Accounting Policies [Line Items]
Weighted-average amortization period				19 years
Trade names and trademarks
Significant Accounting Policies [Line Items]
Weighted-average amortization period				15 years
Southwest Gas Corporation
Significant Accounting Policies [Line Items]
Decrease of net cost of gas sold				$ (1,246,901,000)	(789,216,000)	(430,907,000)
Increase in deferred purchased gas costs				102,765,000	158,975,000	343,728,000
Increase (decrease) of capital expenditures incurred but not yet paid				(20,900,000)	19,700,000	13,900,000
Deferred purchased gas costs				552,885,000	450,120,000
Accrued purchased gas cost				0	207,000,000
Gas pipe materials and operating supplies				83,400,000	77,300,000
Current assets held for sale adjustment				21,376,000	0
Goodwill impairment loss				0	0
Equity AFUDC				1,869,000	0	0
Southwest Gas Corporation | Money Market Funds
Significant Accounting Policies [Line Items]
Money market fund investments				$ 38,600,000	17,600,000
MountainWest
Significant Accounting Policies [Line Items]
Debt portion					86,000
Equity AFUDC					465,000
W.S. Nicholls Western Construction LTD | Centuri
Significant Accounting Policies [Line Items]
VIE ownership percentage				50.00%
Maximum loss exposure amount				$ 12,400,000
Revision of Prior Period, Error Correction, Adjustment
Significant Accounting Policies [Line Items]
Decrease of net cost of gas sold					$ 5,700,000	$ 2,300,000
Increase in deferred purchased gas costs			8,000,000
Loss on disposal adjustment			(21,000,000)
Impairment of asset held for sale adjustment			21,000,000
Discontinued Operations, Disposed of by Sale | MountainWest
Significant Accounting Policies [Line Items]
Ownership percentage disposed				100.00%
Discontinued operation, consideration				$ 1,500,000,000
Disposal Group, Held-for-sale, Not Discontinued Operations | MountainWest
Significant Accounting Policies [Line Items]
Ownership percentage disposed					100.00%
Discontinued operation, consideration					$ 1,500,000,000
Loss on disposal adjustment		$ (28,400,000)	$ (21,000,000)	$ (21,000,000)