- Condensed Consolidating Statement of Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Consolidating Financial Statements
Operating revenue	$ 176,878	$ 232,537	$ 179,031	$ 126,111	$ 167,417	$ 221,288	$ 174,938	$ 134,553	$ 714,557	$ 698,196	$ 676,113
Operations:
Purchased water									212,461	207,103	199,081
Purchased power									31,362	31,080	28,862
Pump taxes									11,518	14,664	13,924
Administrative and general									108,617	100,781	93,326
Other operations									90,061	79,868	74,448
Maintenance									26,834	24,494	22,530
Depreciation and amortization									89,220	83,781	76,783
Income tax (benefit) expense									16,280	18,589	35,279
Property and other taxes									28,792	27,296	24,797
Total operating expenses									615,145	587,656	569,030
Net operating income	20,356	51,567	27,013	476	26,536	47,329	26,839	9,836	99,412	110,540	107,083
Other income and expenses:
Non-regulated revenue									19,205	18,272	15,898
Non-regulated expenses									(13,869)	(22,787)	(9,390)
Other components of net periodic benefit cost									(5,733)	(9,308)	(9,588)
Allowance for equity funds used during construction									6,685	3,954	3,750
Gain on sale of non-utility property									28	50	663
Income tax (expense) benefit on other income and expenses									(1,391)	2,717	(1,548)
Net other income (loss)									4,925	(7,102)	(215)
Interest expense:
Interest expense									44,891	39,917	36,288
Allowance for borrowed funds used during construction									(3,670)	(2,063)	(2,360)
Net interest expense									41,221	37,854	33,928
Equity earnings of subsidiaries									0	0	0
Net income	$ 11,336	$ 42,424	$ 16,996	$ (7,640)	$ 15,368	$ 36,173	$ 14,805	$ (762)	63,116	65,584	72,940
Consolidating Adjustments
Condensed Consolidating Financial Statements
Operating revenue									0	0	0
Operations:
Purchased water									0	0	0
Purchased power									0	0	0
Pump taxes									0	0	0
Administrative and general									0	0	0
Other operations									(583)	(583)	(524)
Maintenance									0	0	0
Depreciation and amortization									(82)	(87)	(91)
Income tax (benefit) expense									858	923	1,059
Property and other taxes									0	0	0
Total operating expenses									193	253	444
Net operating income									(193)	(253)	(444)
Other income and expenses:
Non-regulated revenue									(2,983)	(2,916)	(2,509)
Non-regulated expenses									0	0	0
Other components of net periodic benefit cost									0	0	0
Allowance for equity funds used during construction									0	0	0
Gain on sale of non-utility property									0	0	0
Income tax (expense) benefit on other income and expenses									835	816	1,022
Net other income (loss)									(2,148)	(2,100)	(1,487)
Interest expense:
Interest expense									(2,401)	(2,333)	(1,985)
Allowance for borrowed funds used during construction									0	0	0
Net interest expense									(2,401)	(2,333)	(1,985)
Equity earnings of subsidiaries									(62,745)	(64,748)	(72,487)
Net income									(62,685)	(64,768)	(72,433)
Parent Company
Other income and expenses:
Allowance for equity funds used during construction											0
Gain on sale of non-utility property											0
Interest expense:
Equity earnings of subsidiaries											72,487
Net income											72,940
Parent Company | Reportable Legal Entities
Condensed Consolidating Financial Statements
Operating revenue									0	0	0
Operations:
Purchased water									0	0	0
Purchased power									0	0	0
Pump taxes									0	0	0
Administrative and general									23	0	0
Other operations									0	0	0
Maintenance									0	0	0
Depreciation and amortization									94	94	94
Income tax (benefit) expense									(528)	(960)	(498)
Property and other taxes									0	0	(4)
Total operating expenses									(411)	(866)	(408)
Net operating income									411	866	408
Other income and expenses:
Non-regulated revenue									2,401	2,333	1,985
Non-regulated expenses									0	0	0
Other components of net periodic benefit cost									0	0	0
Allowance for equity funds used during construction									0	0	0
Gain on sale of non-utility property									0	0	0
Income tax (expense) benefit on other income and expenses									(672)	(652)	(809)
Net other income (loss)									1,729	1,681	1,176
Interest expense:
Interest expense									1,769	1,711	1,131
Allowance for borrowed funds used during construction									0	0	0
Net interest expense									1,769	1,711	1,131
Equity earnings of subsidiaries									62,745	64,748	72,487
Net income									63,116	65,584	72,940
Cal Water
Other income and expenses:
Allowance for equity funds used during construction											3,750
Gain on sale of non-utility property											663
Interest expense:
Equity earnings of subsidiaries											0
Net income											70,071
Cal Water | Reportable Legal Entities
Condensed Consolidating Financial Statements
Operating revenue									669,769	656,939	635,604
Operations:
Purchased water									211,998	206,675	198,682
Purchased power									22,338	22,460	21,021
Pump taxes									11,518	14,664	13,924
Administrative and general									98,675	90,563	83,163
Other operations									83,148	73,521	67,069
Maintenance									25,720	23,573	21,595
Depreciation and amortization									83,183	78,601	72,327
Income tax (benefit) expense									14,677	17,678	33,313
Property and other taxes									25,601	24,190	21,778
Total operating expenses									576,858	551,925	532,872
Net operating income									92,911	105,014	102,732
Other income and expenses:
Non-regulated revenue									18,080	17,658	14,608
Non-regulated expenses									(12,526)	(22,122)	(8,139)
Other components of net periodic benefit cost									(5,559)	(8,886)	(9,032)
Allowance for equity funds used during construction									6,685	3,954	3,750
Gain on sale of non-utility property									28	50	663
Income tax (expense) benefit on other income and expenses									(1,476)	2,616	(1,714)
Net other income (loss)									5,232	(6,730)	136
Interest expense:
Interest expense									43,104	38,288	35,116
Allowance for borrowed funds used during construction									(3,408)	(1,909)	(2,319)
Net interest expense									39,696	36,379	32,797
Equity earnings of subsidiaries									0	0	0
Net income									58,447	61,905	70,071
All Other Subsidiaries
Other income and expenses:
Allowance for equity funds used during construction											0
Gain on sale of non-utility property											0
Interest expense:
Equity earnings of subsidiaries											0
Net income											2,362
All Other Subsidiaries | Reportable Legal Entities
Condensed Consolidating Financial Statements
Operating revenue									44,788	41,257	40,509
Operations:
Purchased water									463	428	399
Purchased power									9,024	8,620	7,841
Pump taxes									0	0	0
Administrative and general									9,919	10,218	10,163
Other operations									7,496	6,930	7,903
Maintenance									1,114	921	935
Depreciation and amortization									6,025	5,173	4,453
Income tax (benefit) expense									1,273	948	1,405
Property and other taxes									3,191	3,106	3,023
Total operating expenses									38,505	36,344	36,122
Net operating income									6,283	4,913	4,387
Other income and expenses:
Non-regulated revenue									1,707	1,197	1,814
Non-regulated expenses									(1,343)	(665)	(1,251)
Other components of net periodic benefit cost									(174)	(422)	(556)
Allowance for equity funds used during construction									0	0	0
Gain on sale of non-utility property									0	0	0
Income tax (expense) benefit on other income and expenses									(78)	(63)	(47)
Net other income (loss)									112	47	(40)
Interest expense:
Interest expense									2,419	2,251	2,026
Allowance for borrowed funds used during construction									(262)	(154)	(41)
Net interest expense									2,157	2,097	1,985
Equity earnings of subsidiaries									0	0	0
Net income									$ 4,238	$ 2,863	$ 2,362