Taxes on Income - Reconciliation of Effective Tax Rates (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Amount
Federal taxes on pretax income at statutory rate	$ 35,658	$ 31,383	$ 34,969
State income tax, net of federal benefit*	7,664	6,508	9,785
Tax credits	(68)	(69)	(71)
Nontaxable or nondeductible items	545	508	548
Excess deferred tax amortization	(608)	(1,467)	(1,648)
Flow-through on removal costs	(3,721)	(3,096)	(2,255)
Excess deferred tax adjustment - change in estimate	0	(5,015)	0
Other- net	(114)	1,421	271
Total income tax expense operations	$ 39,356	$ 30,173	$ 41,599
Percent
Tax at U.S. federal statutory tax rate	21.00%	21.00%	21.00%
State income tax, net of federal benefit, percent	4.50%	4.40%	5.90%
Tax credits	0.00%	0.00%	0.00%
Nontaxable or nondeductible items	0.30%	0.30%	0.30%
Excess deferred tax amortization	(0.40%)	(1.00%)	(1.00%)
Flow-through on removal costs	(2.20%)	(2.10%)	(1.40%)
Excess deferred tax adjustment - change in estimate	0.00%	(3.40%)	0.00%
Other-net, percent	0.00%	1.00%	0.20%
Effective income tax rate	(23.20%)	(20.20%)	(25.00%)
GSWC
Amount
Federal taxes on pretax income at statutory rate	$ 27,824	$ 24,640	$ 29,063
State income tax, net of federal benefit*	7,159	5,772	9,169
Tax credits	(68)	(69)	(71)
Nontaxable or nondeductible items	638	582	597
Excess deferred tax amortization	(527)	(1,491)	(1,681)
Flow-through on removal costs	(3,393)	(3,029)	(2,225)
Excess deferred tax adjustment - change in estimate	0	(5,015)	0
Other- net	(83)	1,479	837
Total income tax expense operations	$ 31,550	$ 22,869	$ 35,689
Percent
Tax at U.S. federal statutory tax rate	21.00%	21.00%	21.00%
State income tax, net of federal benefit, percent	5.40%	4.90%	6.60%
Tax credits	(0.10%)	(0.10%)	(0.10%)
Nontaxable or nondeductible items	0.50%	0.50%	0.40%
Excess deferred tax amortization	(0.40%)	(1.30%)	(1.20%)
Flow-through on removal costs	(2.50%)	(2.60%)	(1.60%)
Excess deferred tax adjustment - change in estimate	0.00%	(4.30%)	0.00%
Other-net, percent	(0.10%)	1.40%	0.70%
Effective income tax rate	(23.80%)	(19.50%)	(25.80%)