Stock-Based Compensation Plans - Recognition of Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Stock compensation plans
Immediate vesting for employees of certain age and above	55 years
Stock-based compensation recognized in the income statement, before taxes	$ 3,559	$ 3,744	$ 3,298
Capitalized equity-based compensation cost	500	400	500
GSWC
Stock compensation plans
Stock-based compensation recognized in the income statement, before taxes	3,131	3,279	2,994
Capitalized equity-based compensation cost	500	400	500
Restricted Stock Units | Employees and directors
Stock compensation plans
Stock-based compensation recognized in the income statement, before taxes	3,559	3,744	3,298
Restricted Stock Units | Employees and directors | GSWC
Stock compensation plans
Stock-based compensation recognized in the income statement, before taxes	3,131	3,279	2,994
Nonqualified stock options
Stock compensation plans
Tax benefits from exercise of stock-based awards	900	900	800
Nonqualified stock options | GSWC
Stock compensation plans
Tax benefits from exercise of stock-based awards	$ 900	$ 900	$ 800
2000 and 2008 Employee Plans | Restricted Stock Units
Stock compensation plans
Percentage of rights vesting in the first two years from the date of grant	33.00%
Percentage of rights vesting in the third year from the date of grant	34.00%
2000 and 2008 Employee Plans | Nonqualified stock options
Stock compensation plans
Percentage of rights vesting in the third year from the date of grant	34.00%
2000 and 2008 Employee Plans | Performance awards
Stock compensation plans
Percentage of rights vesting in the first two years from the date of grant	33.00%
Percentage of rights vesting in the third year from the date of grant	34.00%