Earnings per Share/Capital Stock - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Capital stock
Options outstanding (in shares)	0		0	0	0
Issuances of Common Shares under stock-based compensation plans				14,358	19,742
Other financing activities				$ (899)	$ (1,205)
Dividends paid				$ 29,394	$ 26,974
Common Stock, Dividends, Per Share, Cash Paid	$ 0.3975		$ 0.3650	$ 0.7950	$ 0.7300
Parent Company
Capital stock
Dividends paid	$ 14,700		$ 13,500	$ 29,400	$ 27,000
GSWC
Capital stock
Issuances of Common Shares under stock-based compensation plans		1
Other financing activities				(821)	(1,103)
Dividends paid	$ 14,700		$ 13,500	$ 39,400	$ 27,000
Issuance of common share to parent		$ 10,000
Restricted Stock
Capital stock
Restricted stock units outstanding (in shares)	110,576		100,820	110,576	100,820