Background, Organization, and Summary of Significant Accounting Policies - Other Income (Deductions) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Other income (deductions)
Equity AFUDC	$ 246	$ 0	$ 664	$ 0	$ 664	$ 0
Miscellaneous income and (expense)	(773)	1,115	(2,124)	778	(2,046)	687
Foreign transaction gain (loss)	(182)	(7)	35	(19)	32	(19)
Equity in earnings of unconsolidated investments	624	67	1,867	168	1,925	159
Total other income (deductions)	1,593	(3,112)	2	(3,975)	478	282
Southwest Gas Corporation
Other income (deductions)
Change in COLI policies	(1,500)	0	(8,700)	5,800	(5,700)	14,000
Interest income	4,356	1,365	10,355	3,312	12,156	4,113
Equity AFUDC	91	0	248	0	248	1,311
Other components of net periodic benefit cost	(188)	(3,506)	(563)	(10,516)	(4,068)	(15,522)
Miscellaneous income and (expense)	(1,081)	(2,146)	(1,780)	(3,498)	(2,733)	(4,447)
Total other income (deductions)	$ 1,678	$ (4,287)	$ (440)	$ (4,902)	$ (97)	$ (545)