Condensed Consolidating Financial Statements - Condensed Consolidating Statement of Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Condensed Consolidating Financial Statements
Operating revenue	$ 132,247	$ 122,036
Operations:
Water production costs	47,606	42,068
Administrative and general	26,319	22,746
Other operations	17,640	16,124
Maintenance	5,439	6,112
Depreciation and amortization	20,715	19,201
Income tax (benefit) expense	(229)	(884)
Property and other taxes	6,704	6,116
Total operating expenses	124,194	111,483
Net operating income	8,053	10,553
Other income and expenses:
Non-regulated revenue	4,419	3,462
Non-regulated expenses	(5,437)	(2,054)
Other components of net periodic benefit cost	(2,546)	(2,503)
Allowance for equity funds used during construction	911	779
Income tax expense on other income and expenses	758	(889)
Net other income	(1,895)	(1,205)
Interest expense:
Interest expense	9,198	8,710
Allowance for borrowed funds used during construction	(495)	(494)
Net interest expense	8,703	8,216
Equity earnings of subsidiaries	0	0
Net income	(2,545)	1,132
Consolidating Adjustments
Condensed Consolidating Financial Statements
Operating revenue	0	0
Operations:
Water production costs	0	0
Administrative and general	0	0
Other operations	(146)	(126)
Maintenance	0	0
Depreciation and amortization	(22)	(23)
Income tax (benefit) expense	197	257
Property and other taxes	0	0
Total operating expenses	29	108
Net operating income	(29)	(108)
Other income and expenses:
Non-regulated revenue	(676)	(608)
Non-regulated expenses	0	0
Other components of net periodic benefit cost	0	0
Allowance for equity funds used during construction	0	0
Income tax expense on other income and expenses	189	248
Net other income	(487)	(360)
Interest expense:
Interest expense	(531)	(481)
Allowance for borrowed funds used during construction	0	0
Net interest expense	(531)	(481)
Equity earnings of subsidiaries	2,725	(998)
Net income	2,740	(985)
Parent Company | Reportable Legal Entities
Condensed Consolidating Financial Statements
Operating revenue	0	0
Operations:
Water production costs	0	0
Administrative and general	0	0
Other operations	0	0
Maintenance	0	0
Depreciation and amortization	23	23
Income tax (benefit) expense	(78)	(103)
Property and other taxes	0	(4)
Total operating expenses	(55)	(84)
Net operating income	55	84
Other income and expenses:
Non-regulated revenue	531	481
Non-regulated expenses	0	0
Other components of net periodic benefit cost	0	0
Allowance for equity funds used during construction	0	0
Income tax expense on other income and expenses	(148)	(196)
Net other income	383	285
Interest expense:
Interest expense	258	235
Allowance for borrowed funds used during construction	0	0
Net interest expense	258	235
Equity earnings of subsidiaries	(2,725)	998
Net income	(2,545)	1,132
Cal Water | Reportable Legal Entities
Condensed Consolidating Financial Statements
Operating revenue	123,570	113,342
Operations:
Water production costs	45,623	40,189
Administrative and general	23,606	20,126
Other operations	16,217	14,400
Maintenance	5,244	5,906
Depreciation and amortization	19,613	18,111
Income tax (benefit) expense	(340)	(946)
Property and other taxes	6,007	5,412
Total operating expenses	115,970	103,198
Net operating income	7,600	10,144
Other income and expenses:
Non-regulated revenue	4,244	3,135
Non-regulated expenses	(5,293)	(1,747)
Other components of net periodic benefit cost	(2,447)	(2,350)
Allowance for equity funds used during construction	911	779
Income tax expense on other income and expenses	741	(883)
Net other income	(1,844)	(1,066)
Interest expense:
Interest expense	8,934	8,470
Allowance for borrowed funds used during construction	(458)	(476)
Net interest expense	8,476	7,994
Equity earnings of subsidiaries	0	0
Net income	(2,720)	1,084
All Other Subsidiaries | Reportable Legal Entities
Condensed Consolidating Financial Statements
Operating revenue	8,677	8,694
Operations:
Water production costs	1,983	1,879
Administrative and general	2,713	2,620
Other operations	1,569	1,850
Maintenance	195	206
Depreciation and amortization	1,101	1,090
Income tax (benefit) expense	(8)	(92)
Property and other taxes	697	708
Total operating expenses	8,250	8,261
Net operating income	427	433
Other income and expenses:
Non-regulated revenue	320	454
Non-regulated expenses	(144)	(307)
Other components of net periodic benefit cost	(99)	(153)
Allowance for equity funds used during construction	0	0
Income tax expense on other income and expenses	(24)	(58)
Net other income	53	(64)
Interest expense:
Interest expense	537	486
Allowance for borrowed funds used during construction	(37)	(18)
Net interest expense	500	468
Equity earnings of subsidiaries	0	0
Net income	$ (20)	$ (99)