CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Income Statement [Abstract]
Operating revenue	$ 1,000,140	$ 1,036,806	$ 794,632
Operations:
Purchased water	252,897	241,201	223,833
Purchased power	45,106	47,690	45,656
Pump taxes	24,234	21,757	19,023
Administrative and general	141,571	139,515	142,235
Other operations	130,106	118,457	112,481
Maintenance	36,001	34,753	31,975
Depreciation and amortization	144,365	131,901	121,212
Income tax expense (benefit)	11,216	35,938	(15,189)
Property and other taxes	44,275	40,540	36,271
Total operating expenses	829,771	811,752	717,497
Net operating income	170,369	225,054	77,135
Other income and expenses:
Non-regulated revenue	20,776	20,628	18,509
Non-regulated expenses	(14,649)	(14,201)	(11,807)
Other components of net periodic benefit credit	18,230	15,803	20,215
Allowance for equity funds used during construction	7,709	6,902	5,551
Income tax expense on other income and expenses	(7,890)	(6,551)	(8,408)
Net other income	24,176	22,581	24,060
Interest expense:
Interest expense	70,392	60,698	52,809
Allowance for borrowed funds used during construction	(3,695)	(3,148)	(2,990)
Net interest expense	66,697	57,550	49,819
Net income	127,848	190,085	51,376
Net loss attributable to noncontrolling interest	(363)	(722)	(535)
Net income attributable to California Water Service Group	$ 128,211	$ 190,807	$ 51,911
Earnings per share:
Basic (in dollars per share)	$ 2.15	$ 3.26	$ 0.91
Diluted (in dollars per share)	$ 2.15	$ 3.25	$ 0.91
Weighted average number of common shares outstanding:
Basic (in shares)	59,570	58,612	56,952
Diluted (in shares)	59,633	58,647	56,983