Background, Organization, and Summary of Significant Accounting Policies - Narrative (Details) - USD ($)	1 Months Ended			3 Months Ended		12 Months Ended
	Apr. 30, 2024	Apr. 30, 2023	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Apr. 22, 2024	Mar. 31, 2022	Nov. 30, 2018
Significant Accounting Policies [Line Items]
Common stock, par (in USD per share)				$ 1		$ 1
Decrease of net cost of gas sold				$ (629,997,000)	$ (507,537,000)
Increase in deferred purchased gas costs				(354,203,000)	535,224,000
Other property and investments adjustment				(1,252,861,000)		$ (1,266,340,000)
Current assets held for sale				0		21,377,000
Decrease of capital expenditures incurred but not yet paid				20,800,000	37,300,000
Goodwill impairment loss				0
Dividends declared but not yet paid				44,400,000		44,400,000
Accrued purchased gas cost				120,300,000		87,600,000
Deferred purchased gas costs			$ 970,000,000	$ 198,682,000	$ 970,000,000	552,885,000
Percentage of redeemable noncontrolling interest redeemed			5.00%
Effective income tax rate				16.30%	37.60%
Promissory Note | Prime Rate
Significant Accounting Policies [Line Items]
Debt, basis spread on variable rate				2.00%
Drum
Significant Accounting Policies [Line Items]
Ownership percentage by noncontrolling owners				0.81%
Money Market Funds
Significant Accounting Policies [Line Items]
Money market fund investments				$ 407,400,000		48,900,000
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			$ 27,000,000		27,000,000
Estimated loss on disposition of assets						5,200,000
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
Decrease in net cost of gas sold					8,000,000
Loss on disposal adjustment					21,000,000
Impairment of asset held for sale adjustment					21,000,000
Subsequent Event
Significant Accounting Policies [Line Items]
Payments to noncontrolling interests	$ 92,000,000
Subsequent Event | Centuri
Significant Accounting Policies [Line Items]
Ownership percentage by parent									81.00%
Centuri
Significant Accounting Policies [Line Items]
Payment for repurchase of redeemable noncontrolling interest		$ 39,900,000
Centuri | Drum
Significant Accounting Policies [Line Items]
Percentage of equity interest exchanged with debt forgiveness				0.47%
Equity ownership, percentage purchased				0.13%
Payments to acquire additional interest				$ 800,000
Centuri | Drum
Significant Accounting Policies [Line Items]
Ownership percentage by parent				99.00%
Centuri | Subsequent Event | IPO
Significant Accounting Policies [Line Items]
Sale of stock, number of shares (in shares)	14,260,000
Common stock, par (in USD per share)									$ 0.01
Shares issued, price per share (in USD per share)									$ 21.00
Centuri | Subsequent Event | Private Placement
Significant Accounting Policies [Line Items]
Sale of stock, number of shares (in shares)	2,591,929
Southwest Gas Corporation
Significant Accounting Policies [Line Items]
Decrease of net cost of gas sold				$ (629,997,000)	(501,169,000)
Increase in deferred purchased gas costs				(354,203,000)	520,219,000
Other property and investments adjustment				(156,262,000)		(152,658,000)
Current assets held for sale				0		21,376,000
Decrease of capital expenditures incurred but not yet paid				9,600,000	$ 34,200,000
Gas pipe materials and operating supplies				80,900,000		83,400,000
Deferred purchased gas costs				$ 198,682,000		552,885,000
Effective income tax rate				18.20%	18.30%
Southwest Gas Corporation | Money Market Funds
Significant Accounting Policies [Line Items]
Money market fund investments				$ 407,200,000		$ 38,600,000
Previous Owner Of Linetec | Linetec
Significant Accounting Policies [Line Items]
Ownership percentage by noncontrolling owners		10.00%		10.00%						15.00%	20.00%
Current partial redemption transpired				$ 92,000,000
Certain Members Of Riggs Distler Management | Drum
Significant Accounting Policies [Line Items]
Ownership percentage by noncontrolling owners				1.41%
Discontinued Operations, Disposed of by Sale | MountainWest
Significant Accounting Policies [Line Items]
Ownership percentage disposed							100.00%
Disposal consideration							$ 1,500,000,000