Earnings Per Share of Common Stock (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2022	Jun. 30, 2021
Earnings Per Share [Abstract]
Net income	$ 19,215	$ 894	$ 38,076	$ (3,032)	$ 20,109	$ 35,044
Net loss attributable to noncontrolling interests	(269)		(149)		(461)	(149)
Net income attributable to California Water Service Group	$ 19,484		$ 38,225		$ 20,570	$ 35,193
Weighted average common shares outstanding, basic (in shares)	54,007		51,080		53,870	50,762
Diluted (in shares)	54,042		51,080		53,918	50,762
Earnings per share of common stock - basic (in dollars per share)	$ 0.36		$ 0.75		$ 0.38	$ 0.69
Earnings per share of common stock - diluted (in dollars per share)	$ 0.36		$ 0.75		$ 0.38	$ 0.69