Earnings per Share/Capital Stock - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Capital stock
Options outstanding (in shares)	0	0
Other financing activities	$ (1,111,000)	$ (883,000)
Dividends paid	$ 15,905,000	$ 14,695,000
Common Stock, Dividends, Per Share, Cash Paid	$ 0.4300	$ 0.3975
Issuance of common share	$ 15,584,000
Sale of stock, number of shares issued in transaction (in shares)	227,981
Payments for commissions	$ 247,000
Sale of stock, consideration received on transaction	$ 16,200,000
Issuances of Common Shares under stock-based compensation plans	20,290	14,043
Parent Company
Capital stock
Dividends paid	$ 15,900,000	$ 14,700,000
GSWC
Capital stock
Issuances of Common Shares from an at-the-market program, net of issuance costs		1
Other financing activities	(1,040,000)	$ (808,000)
Dividends paid	$ 0	24,700,000
Issuance of common share		$ 10,000,000
Restricted Stock
Capital stock
Restricted stock units outstanding (in shares)	128,668	106,817