Condensed Consolidating Financial Statements - Condensed Consolidating Statement of (Loss) Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Condensed Consolidating Financial Statements
Operating revenue	$ 175,484	$ 179,031	$ 301,047	$ 305,142
Operations:
Water production costs	71,142	64,635	125,118	110,227
Administrative and general	26,939	25,434	56,619	54,531
Other operations	25,898	22,542	39,872	40,363
Maintenance	6,722	5,692	13,795	12,147
Depreciation and amortization	24,542	22,326	49,034	44,694
Income tax (benefit) expense	622	4,321	(3,315)	1,330
Property and other taxes	7,126	7,068	14,354	14,361
Total operating (income) expenses	162,991	152,018	295,477	277,653
Net operating income	12,493	27,013	5,570	27,489
Other income and expenses:
Non-regulated revenue	4,208	5,130	8,035	10,031
Non-regulated expenses	(492)	(3,900)	(8,946)	(6,119)
Other components of net periodic benefit cost	(1,332)	(1,192)	(2,762)	(2,451)
Allowance for equity funds used during construction	1,705	1,686	3,319	3,219
Income tax expense on other income and expenses	(820)	(487)	93	(1,315)
Net other income	3,269	1,237	(261)	3,365
Interest expense:
Interest expense	11,613	12,178	22,411	23,253
Allowance for borrowed funds used during construction	(1,132)	(924)	(2,076)	(1,755)
Net interest expense	10,481	11,254	20,335	21,498
Equity earnings of subsidiaries	0	0	0	0
Net income	5,281	16,996	(15,026)	9,356
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	(146)	(144)	(292)	(290)
Maintenance	0	0	0	0
Depreciation and amortization	(19)	(20)	(39)	(41)
Income tax (benefit) expense	198	218	400	436
Property and other taxes	0	0	0	0
Total operating (income) expenses	33	54	69	105
Net operating income	(33)	(54)	(69)	(105)
Other income and expenses:
Non-regulated revenue	(690)	(759)	(1,390)	(1,518)
Non-regulated expenses	0	0	0	0
Other components of net periodic benefit cost	0	0	0	0
Allowance for equity funds used during construction	0	0	0	0
Income tax expense on other income and expenses	193	213	389	425
Net other income	(497)	(546)	(1,001)	(1,093)
Interest expense:
Interest expense	(545)	(614)	(1,099)	(1,227)
Allowance for borrowed funds used during construction	0	0	0	0
Net interest expense	(545)	(614)	(1,099)	(1,227)
Equity earnings of subsidiaries	(5,174)	(16,923)	15,230	(9,189)
Net income	(5,159)	(16,909)	15,259	(9,160)
Parent Company | Reportable Legal Entities
Condensed Consolidating Financial Statements
Operating revenue	0	0	0	0
Operations:
Water production costs	0	0	0	0
Administrative and general	0	23	0	23
Other operations	0	0	0	0
Maintenance	0	0	0	0
Depreciation and amortization	23	24	47	47
Income tax (benefit) expense	(110)	(144)	(228)	(279)
Property and other taxes	0	0	0	0
Total operating (income) expenses	(87)	(97)	(181)	(209)
Net operating income	87	97	181	209
Other income and expenses:
Non-regulated revenue	544	614	1,099	1,227
Non-regulated expenses	0	0	0	0
Other components of net periodic benefit cost	0	0	0	0
Allowance for equity funds used during construction	0	0	0	0
Income tax expense on other income and expenses	(153)	(171)	(308)	(343)
Net other income	391	443	791	884
Interest expense:
Interest expense	371	467	768	926
Allowance for borrowed funds used during construction	0	0	0	0
Net interest expense	371	467	768	926
Equity earnings of subsidiaries	5,174	16,923	(15,230)	9,189
Net income	5,281	16,996	(15,026)	9,356
Cal Water | Reportable Legal Entities
Condensed Consolidating Financial Statements
Operating revenue	164,282	167,450	279,674	283,524
Operations:
Water production costs	68,898	62,143	120,656	105,569
Administrative and general	24,331	23,207	51,223	49,410
Other operations	23,960	20,857	36,115	36,979
Maintenance	6,459	5,423	13,108	11,646
Depreciation and amortization	22,945	20,814	45,902	41,701
Income tax (benefit) expense	289	3,792	(3,733)	687
Property and other taxes	6,244	6,305	12,670	12,811
Total operating (income) expenses	153,126	142,541	275,941	258,803
Net operating income	11,156	24,909	3,733	24,721
Other income and expenses:
Non-regulated revenue	3,923	4,881	7,514	9,509
Non-regulated expenses	(288)	(3,665)	(8,543)	(5,703)
Other components of net periodic benefit cost	(1,300)	(1,164)	(2,701)	(2,393)
Allowance for equity funds used during construction	1,705	1,686	3,319	3,219
Income tax expense on other income and expenses	(808)	(486)	110	(1,296)
Net other income	3,232	1,252	(301)	3,336
Interest expense:
Interest expense	11,240	11,708	21,640	22,321
Allowance for borrowed funds used during construction	(1,084)	(862)	(1,973)	(1,638)
Net interest expense	10,156	10,846	19,667	20,683
Equity earnings of subsidiaries	0	0	0	0
Net income	4,232	15,315	(16,235)	7,374
All Other Subsidiaries | Reportable Legal Entities
Condensed Consolidating Financial Statements
Operating revenue	11,202	11,581	21,373	21,618
Operations:
Water production costs	2,244	2,492	4,462	4,658
Administrative and general	2,608	2,204	5,396	5,098
Other operations	2,084	1,829	4,049	3,674
Maintenance	263	269	687	501
Depreciation and amortization	1,593	1,508	3,124	2,987
Income tax (benefit) expense	245	455	246	486
Property and other taxes	882	763	1,684	1,550
Total operating (income) expenses	9,919	9,520	19,648	18,954
Net operating income	1,283	2,061	1,725	2,664
Other income and expenses:
Non-regulated revenue	431	394	812	813
Non-regulated expenses	(204)	(235)	(403)	(416)
Other components of net periodic benefit cost	(32)	(28)	(61)	(58)
Allowance for equity funds used during construction	0	0	0	0
Income tax expense on other income and expenses	(52)	(43)	(98)	(101)
Net other income	143	88	250	238
Interest expense:
Interest expense	547	617	1,102	1,233
Allowance for borrowed funds used during construction	(48)	(62)	(103)	(117)
Net interest expense	499	555	999	1,116
Equity earnings of subsidiaries	0	0	0	0
Net income	$ 927	$ 1,594	$ 976	$ 1,786