Earnings Per Share of Common Stock (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2022	Sep. 30, 2021
Earnings Per Share [Abstract]
Net income	$ 55,683	$ 19,215	$ 894	$ 62,499	$ 38,076	$ (3,032)	$ 75,792	$ 97,543
Net (loss) income attributable to noncontrolling interests	(189)			70			(650)	(79)
Net income attributable to California Water Service Group	$ 55,872			$ 62,429			$ 76,442	$ 97,622
Weighted average common shares outstanding, basic (in shares)	54,007			51,823			54,063	51,119
Weighted average common shares outstanding, diluted (in shares)	54,042			51,823			54,104	51,119
Earnings per share of common stock - basic (in dollars per share)	$ 1.03			$ 1.20			$ 1.41	$ 1.91
Earnings per share of common stock - diluted (in dollars per share)	$ 1.03			$ 1.20			$ 1.41	$ 1.91