Earnings (Loss) Per Share of Common Stock (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Earnings Per Share [Abstract]
Net income (loss)	$ 894	$ (3,032)
Net loss attributable to noncontrolling interests	(192)	0
Net income (loss) attributable to California Water Service Group	$ 1,086	$ (3,032)
Weighted average common shares outstanding, basic (in shares)	53,731	50,440
Diluted (in shares)	53,775	50,440
Earnings (loss) per share of common stock - basic (in dollars per share)	$ 0.02	$ (0.06)
Earnings (loss) per share of common stock - diluted (in dollars per share)	$ 0.02	$ (0.06)