Condensed Consolidating Financial Statements - Condensed Consolidating Statement of Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Condensed Consolidating Financial Statements
Operating revenue	$ 126,111	$ 134,553
Operations:
Water production costs	45,592	47,606
Administrative and general	29,097	26,319
Other operations	17,821	17,640
Maintenance	6,455	5,439
Depreciation and amortization	22,368	20,715
Income tax (benefit) expense	(2,991)	294
Property and other taxes	7,293	6,704
Total operating (income) expenses	125,635	124,717
Net operating income	476	9,836
Other income and expenses:
Non-regulated revenue	4,901	4,419
Non-regulated expenses	(2,219)	(5,437)
Other components of net periodic benefit cost	(1,259)	(2,546)
Allowance for equity funds used during construction	1,533	911
Income tax (expense) benefit on other income and expenses	(828)	758
Net other income (loss)	2,128	(1,895)
Interest expense:
Interest expense	11,075	9,198
Allowance for borrowed funds used during construction	(831)	(495)
Net interest expense	10,244	8,703
Equity earnings of subsidiaries	0	0
Net loss	(7,640)	(762)
Consolidating Adjustments
Condensed Consolidating Financial Statements
Operating revenue	0	0
Operations:
Water production costs	0	0
Administrative and general	0	0
Other operations	(146)	(146)
Maintenance	0	0
Depreciation and amortization	(21)	(22)
Income tax (benefit) expense	218	197
Property and other taxes	0	0
Total operating (income) expenses	51	29
Net operating income	(51)	(29)
Other income and expenses:
Non-regulated revenue	(759)	(676)
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) benefit on other income and expenses	212	189
Net other income (loss)	(547)	(487)
Interest expense:
Interest expense	(613)	(531)
Allowance for borrowed funds used during construction	0	0
Net interest expense	(613)	(531)
Equity earnings of subsidiaries	7,734	942
Net loss	7,749	957
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	(135)	(78)
Property and other taxes	0	0
Total operating (income) expenses	(112)	(55)
Net operating income	112	55
Other income and expenses:
Non-regulated revenue	613	531
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) benefit on other income and expenses	(172)	(148)
Net other income (loss)	441	383
Interest expense:
Interest expense	459	258
Allowance for borrowed funds used during construction	0	0
Net interest expense	459	258
Equity earnings of subsidiaries	(7,734)	(942)
Net loss	(7,640)	(762)
Cal Water | Reportable Legal Entities
Condensed Consolidating Financial Statements
Operating revenue	116,074	125,876
Operations:
Water production costs	43,426	45,623
Administrative and general	26,203	23,606
Other operations	16,122	16,217
Maintenance	6,223	5,244
Depreciation and amortization	20,887	19,613
Income tax (benefit) expense	(3,105)	183
Property and other taxes	6,506	6,007
Total operating (income) expenses	116,262	116,493
Net operating income	(188)	9,383
Other income and expenses:
Non-regulated revenue	4,628	4,244
Non-regulated expenses	(2,038)	(5,293)
Other components of net periodic benefit cost	(1,229)	(2,447)
Allowance for equity funds used during construction	1,533	911
Income tax (expense) benefit on other income and expenses	(810)	741
Net other income (loss)	2,084	(1,844)
Interest expense:
Interest expense	10,613	8,934
Allowance for borrowed funds used during construction	(776)	(458)
Net interest expense	9,837	8,476
Equity earnings of subsidiaries	0	0
Net loss	(7,941)	(937)
All Other Subsidiaries | Reportable Legal Entities
Condensed Consolidating Financial Statements
Operating revenue	10,037	8,677
Operations:
Water production costs	2,166	1,983
Administrative and general	2,894	2,713
Other operations	1,845	1,569
Maintenance	232	195
Depreciation and amortization	1,479	1,101
Income tax (benefit) expense	31	(8)
Property and other taxes	787	697
Total operating (income) expenses	9,434	8,250
Net operating income	603	427
Other income and expenses:
Non-regulated revenue	419	320
Non-regulated expenses	(181)	(144)
Other components of net periodic benefit cost	(30)	(99)
Allowance for equity funds used during construction	0	0
Income tax (expense) benefit on other income and expenses	(58)	(24)
Net other income (loss)	150	53
Interest expense:
Interest expense	616	537
Allowance for borrowed funds used during construction	(55)	(37)
Net interest expense	561	500
Equity earnings of subsidiaries	0	0
Net loss	$ 192	$ (20)