Earnings per Share/Capital Stock - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2024	Mar. 31, 2024	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2024	Jun. 30, 2023
Capital stock
Options outstanding (in shares)	0		0		0	0
Other financing activities					$ (1,138)	$ (899)
Dividends paid					$ 31,929	$ 29,394
Common Stock, Dividends, Per Share, Cash Paid	$ 0.4300		$ 0.3975		$ 0.8600	$ 0.7950
Issuance of Common Shares from an at-the-market program, net of issuance costs	$ 16,724	$ 15,584
Sale of stock, number of shares issued in transaction (in shares)	227,667				455,648
Payments for commissions	$ 300				$ 500
Sale of stock, consideration received on transaction	16,800				$ 33,000
Issuances of Common Shares under stock-based compensation plans (in shares)					20,939	14,358
Parent Company
Capital stock
Dividends paid	$ 16,000		$ 14,700		$ 31,900	$ 29,400
GSWC
Capital stock
Issuance of Common Shares from an at-the-market program, net of issuance costs (in shares)						1
Other financing activities					(1,064)	$ (821)
Dividends paid			14,700		$ 0	39,400
Issuance of Common Shares from an at-the-market program, net of issuance costs				$ 10,000		$ 10,000
ASUS
Capital stock
Dividends paid			$ 16,000
Restricted Stock
Capital stock
Restricted stock units outstanding (in shares)	132,530		110,576		132,530	110,576