Earnings per Share/Capital Stock - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		6 Months Ended		28 Months Ended
	Feb. 27, 2024	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 12, 2026
Capital stock
Sale of stock, maximum consideration on transaction	$ 200,000						$ 200,000
Agreement term (in years)	3 years
Sale of stock, number of shares issued in transaction (in shares)		442,722	0	526,959	334,548	2,575,947
Sale of stock, consideration received on transaction		$ 33,800		$ 40,100	$ 25,800
Payments for commissions		500		600	400
Payments of stock issuance costs		$ 100		$ 200	$ 200
Issuances of Common Shares under stock-based compensation plans (in shares)				26,023	23,463
Payment, tax withholding, share-based payment arrangement				$ 1,374	$ 1,320
Dividends paid				$ 39,494	$ 35,688
Dividends declared per common share (in dollars per share)		$ 0.5040	$ 0.4655	$ 1.0080	$ 0.9310
AWR
Capital stock
Dividends paid		$ 19,800	$ 17,900	$ 39,500	$ 35,700
GSWC
Capital stock
Payment, tax withholding, share-based payment arrangement				1,227	1,183
Dividends paid		11,800	18,000	31,500	18,000
ASUS
Capital stock
Dividends paid		$ 8,000	$ 0	$ 8,000	$ 0
Restricted Stock
Capital stock
Restricted stock units outstanding (in shares)		160,506	158,549	160,506	158,549	160,506