Background, Organization, and Summary of Significant Accounting Policies - Other Income (Deductions) (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Other income (deductions)
Equity AFUDC	$ 182	$ 0	$ 182	$ 0
Foreign transaction gain (loss)	3	(3)	(16)	(9)
Equity in earnings of unconsolidated investments	515	(8)	749	121
Miscellaneous income and (expense)	(771)	(91)	176	(179)
Total other income (deductions)	1,244	448	(2,703)	14,429
Southwest Gas Corporation
Other income (deductions)
Change in COLI policies	(2,000)	2,700	4,100	27,400
Interest income	2,801	716	7,198	3,343
Equity AFUDC	76	981	(905)	4,644
Other components of net periodic benefit cost	(188)	(3,505)	(10,704)	(18,522)
Miscellaneous income and (expense)	626	(342)	(3,483)	(2,369)
Total other income (deductions)	$ 1,315	$ 550	$ (3,794)	$ 14,496