CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income Statement [Abstract]
Operating revenue	$ 213,123	$ 175,484	$ 360,860	$ 301,047
Operations:
Water production costs	74,911	71,142	129,737	125,118
Administrative and general	31,756	26,939	62,125	56,619
Other operations	20,720	25,898	38,632	39,872
Maintenance	6,610	6,722	13,379	13,795
Depreciation and amortization	27,237	24,542	54,284	49,034
Income taxes	1,972	622	1,871	(3,315)
Property and other taxes	7,671	7,126	15,667	14,354
Total operating expenses	170,877	162,991	315,695	295,477
Net operating income	42,246	12,493	45,165	5,570
Other income and expenses:
Non-regulated revenue	5,374	4,208	10,946	8,035
Non-regulated expenses	(1,815)	(492)	(6,575)	(8,946)
Other components of net periodic benefit credit (cost)	2,688	(1,332)	5,667	(2,762)
Allowance for equity funds used during construction	848	1,705	1,392	3,319
Income tax expense on other income and expenses	(512)	(820)	(870)	93
Net other income	6,583	3,269	10,560	(261)
Interest expense:
Interest expense	11,206	11,613	21,428	22,411
Allowance for borrowed funds used during construction	(453)	(1,132)	(747)	(2,076)
Net interest expense	10,753	10,481	20,681	20,335
Net income	38,076	5,281	35,044	(15,026)
Loss attributable to noncontrolling interests	149	0	149	0
Net income attributable to California Water Service Group	$ 38,225	$ 5,281	$ 35,193	$ (15,026)
Earnings per share of common stock:
Basic (in dollars per share)	$ 0.75	$ 0.11	$ 0.69	$ (0.31)
Diluted (in dollars per share)	$ 0.75	$ 0.11	$ 0.69	$ (0.31)
Weighted average shares outstanding:
Basic (in shares)	51,080	48,936	50,762	48,759
Diluted (in shares)	51,080	48,936	50,762	48,759