Taxes on Income - Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024
Deferred tax assets:
Regulatory-liability-related	$ 28,871	$ 28,851
Contributions and advances	7,389	6,768
Other	8,077	5,801
Total deferred tax assets	44,337	41,420
Deferred tax liabilities:
Fixed assets	(176,142)	(169,666)
Regulatory-asset-related: depreciation and other	(52,909)	(43,149)
Balancing and memorandum accounts (non-flow-through)	(9,407)	(8,778)
Total deferred tax liabilities	(238,458)	(221,593)
Accumulated deferred income taxes - net	(194,121)	(180,173)
GSWC
Deferred tax assets:
Regulatory-liability-related	27,247	27,171
Contributions and advances	7,546	7,103
Other	7,550	5,632
Total deferred tax assets	42,343	39,906
Deferred tax liabilities:
Fixed assets	(166,841)	(162,366)
Regulatory-asset-related: depreciation and other	(48,136)	(39,635)
Balancing and memorandum accounts (non-flow-through)	(4,657)	(4,315)
Total deferred tax liabilities	(219,634)	(206,316)
Accumulated deferred income taxes - net	$ (177,291)	$ (166,410)