Condensed Consolidating Financial Statements - Condensed Consolidating Statement of Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Condensed Consolidating Financial Statements
Operating revenue	$ 171,132	$ 152,445	$ 293,168	$ 274,172
Operations:
Water production costs	64,131	57,589	106,199	98,658
Administrative and general	23,796	23,366	49,045	51,193
Other operations	18,328	18,903	34,452	38,205
Maintenance	4,708	5,934	10,820	11,997
Depreciation and amortization	19,218	15,842	38,419	31,888
Income tax (benefit) expense	9,635	6,870	8,751	5,945
Property and other taxes	6,057	5,407	12,173	11,482
Total operating (income) expense	145,873	133,911	259,859	249,368
Net operating income (loss)	25,259	18,534	33,309	24,804
Other income and expenses:
Non-regulated revenue	3,739	3,764	7,201	7,192
Non-regulated expenses	(1,614)	(2,809)	(3,668)	(5,789)
Allowance for equity funds used during construction	879	0	1,658	0
Income tax expense on other income and expenses	(1,217)	(384)	(2,106)	(565)
Net other income	1,787	571	3,085	838
Interest expense:
Interest expense	9,079	8,434	17,789	16,499
Allowance for borrowed funds used during construction	(564)	(837)	(1,058)	(1,567)
Net interest expense	8,515	7,597	16,731	14,932
Equity earnings of subsidiaries	0	0	0	0
Net income	18,531	11,508	19,663	10,710
Consolidating Adjustments
Condensed Consolidating Financial Statements
Operating revenue	0	0	0	0
Operations:
Water production costs	0	0	0	0
Administrative and general	0	0	0	0
Other operations	(126)	(84)	(252)	(210)
Maintenance	0	0	0	0
Depreciation and amortization	(23)	(24)	(46)	(48)
Income tax (benefit) expense	263	238	520	495
Property and other taxes	0	0	0	0
Total operating (income) expense	114	130	222	237
Net operating income (loss)	(114)	(130)	(222)	(237)
Other income and expenses:
Non-regulated revenue	(622)	(560)	(1,230)	(1,166)
Non-regulated expenses	0	0	0	0
Allowance for equity funds used during construction	0		0
Income tax expense on other income and expenses	253	228	501	475
Net other income	(369)	(332)	(729)	(691)
Interest expense:
Interest expense	(496)	(476)	(977)	(956)
Allowance for borrowed funds used during construction	0	0	0	0
Net interest expense	(496)	(476)	(977)	(956)
Equity earnings of subsidiaries	(18,415)	(11,371)	(19,413)	(10,434)
Net income	(18,402)	(11,357)	(19,387)	(10,406)
Parent Company
Condensed Consolidating Financial Statements
Operating revenue	0	0	0	0
Operations:
Water production costs	0	0	0	0
Administrative and general	0	0	0	0
Other operations	0	0	0	0
Maintenance	0	0	0	0
Depreciation and amortization	26	57	49	114
Income tax (benefit) expense	(123)	(93)	(226)	(187)
Property and other taxes	0	0	(4)	0
Total operating (income) expense	(97)	(36)	(181)	(73)
Net operating income (loss)	97	36	181	73
Other income and expenses:
Non-regulated revenue	496	462	977	926
Non-regulated expenses	0	0	0	0
Allowance for equity funds used during construction	0		0
Income tax expense on other income and expenses	(202)	(188)	(398)	(377)
Net other income	294	274	579	549
Interest expense:
Interest expense	275	173	510	346
Allowance for borrowed funds used during construction	0	0	0	0
Net interest expense	275	173	510	346
Equity earnings of subsidiaries	18,415	11,371	19,413	10,434
Net income	18,531	11,508	19,663	10,710
Cal Water
Condensed Consolidating Financial Statements
Operating revenue	161,174	142,342	274,516	255,369
Operations:
Water production costs	62,089	55,643	102,278	94,888
Administrative and general	21,147	20,667	43,623	45,610
Other operations	16,729	17,365	31,129	35,091
Maintenance	4,509	5,692	10,415	11,532
Depreciation and amortization	18,102	14,735	36,213	29,650
Income tax (benefit) expense	9,100	6,228	8,154	5,191
Property and other taxes	5,315	4,669	10,727	10,059
Total operating (income) expense	136,991	124,999	242,539	232,021
Net operating income (loss)	24,183	17,343	31,977	23,348
Other income and expenses:
Non-regulated revenue	3,469	3,439	6,604	6,635
Non-regulated expenses	(1,428)	(2,547)	(3,175)	(5,252)
Allowance for equity funds used during construction	879		1,658
Income tax expense on other income and expenses	(1,190)	(364)	(2,073)	(564)
Net other income	1,730	528	3,014	819
Interest expense:
Interest expense	8,795	8,263	17,265	16,162
Allowance for borrowed funds used during construction	(542)	(820)	(1,018)	(1,534)
Net interest expense	8,253	7,443	16,247	14,628
Equity earnings of subsidiaries	0	0	0	0
Net income	17,660	10,428	18,744	9,539
All Other Subsidiaries
Condensed Consolidating Financial Statements
Operating revenue	9,958	10,103	18,652	18,803
Operations:
Water production costs	2,042	1,946	3,921	3,770
Administrative and general	2,649	2,699	5,422	5,583
Other operations	1,725	1,622	3,575	3,324
Maintenance	199	242	405	465
Depreciation and amortization	1,113	1,074	2,203	2,172
Income tax (benefit) expense	395	497	303	446
Property and other taxes	742	738	1,450	1,423
Total operating (income) expense	8,865	8,818	17,279	17,183
Net operating income (loss)	1,093	1,285	1,373	1,620
Other income and expenses:
Non-regulated revenue	396	423	850	797
Non-regulated expenses	(186)	(262)	(493)	(537)
Allowance for equity funds used during construction	0		0
Income tax expense on other income and expenses	(78)	(60)	(136)	(99)
Net other income	132	101	221	161
Interest expense:
Interest expense	505	474	991	947
Allowance for borrowed funds used during construction	(22)	(17)	(40)	(33)
Net interest expense	483	457	951	914
Equity earnings of subsidiaries	0	0	0	0
Net income	$ 742	$ 929	$ 643	$ 867