(Loss) Earnings Per Share of Common Stock (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Earnings Per Share [Abstract]
Net (loss) income	$ (22,334)	$ 894
Net loss attributable to noncontrolling interests	(123)	(192)
Net income attributable to California Water Service Group	$ (22,211)	$ 1,086
Weighted average common shares outstanding, basic (in shares)	55,666	53,731
Weighted average common shares outstanding, dilutive (in shares)	55,666	53,775
(Loss) earnings per share of common stock - basic (in dollars per share)	$ (0.40)	$ 0.02
(Loss) earnings per share of common stock - diluted (in dollars per share)	$ (0.40)	$ 0.02