CONDENSED CONSOLIDATING FINANCIAL STATEMENTS (Details 3) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Consolidating Financial Statements
Operating revenue	$ 167,417	$ 221,288	$ 174,938	$ 134,553	$ 164,296	$ 214,037	$ 173,438	$ 124,342	$ 698,196	$ 676,113	$ 609,370
Operations:
Purchased water									207,103	199,081	181,515
Purchased power									31,080	28,862	27,180
Pump taxes									14,664	13,924	11,298
Administrative and general									100,781	93,326	87,601
Other operations									79,868	74,448	80,082
Maintenance									24,494	22,530	22,993
Depreciation and amortization									83,781	76,783	63,599
Income tax (benefit) expense									18,589	35,279	29,235
Property and other taxes									27,296	24,797	23,231
Total operating expenses									587,656	569,030	526,734
Net operating income	$ 26,536	$ 47,329	$ 26,839	$ 9,836	$ 23,077	$ 43,902	$ 28,111	$ 11,993	110,540	107,083	82,636
Other income and expenses:
Non-regulated revenue									18,272	15,898	16,585
Non-regulated expenses									(22,787)	(9,390)	(11,445)
Other components of net periodic benefit cost									(9,308)	(9,588)	(10,873)
Allowance for equity funds used during construction									3,954	3,750	0
Gain (loss) on sale of non-utility property									50	663	(146)
Income tax benefit (expense) on other income and expenses									2,717	(1,548)	2,419
Net other loss									(7,102)	(215)	(3,460)
Interest expense:
Interest expense									39,917	36,288	33,466
Allowance for borrowed funds used during construction									(2,063)	(2,360)	(2,965)
Net interest expense									37,854	33,928	30,501
Equity earnings of subsidiaries									0	0	0
Net income									65,584	72,940	48,675
Reportable Legal Entities
Interest expense:
Net income									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)	(524)	(505)
Maintenance									0	0	0
Depreciation and amortization									(87)	(91)	(96)
Income tax (benefit) expense									923	1,059	1,010
Property and other taxes									0	0	0
Total operating expenses									253	444	409
Net operating income									(253)	(444)	(409)
Other income and expenses:
Non-regulated revenue									(2,916)	(2,509)	(2,385)
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
Gain (loss) on sale of non-utility property									0	0	0
Income tax benefit (expense) on other income and expenses									816	1,022	972
Net other loss									(2,100)	(1,487)	(1,413)
Interest expense:
Interest expense									(2,333)	(1,985)	(1,879)
Allowance for borrowed funds used during construction									0	0	0
Net interest expense									(2,333)	(1,985)	(1,879)
Equity earnings of subsidiaries									(64,748)	(72,487)	(48,158)
Net income									(64,768)	(72,433)	(48,101)
Parent Company
Other income and expenses:
Gain (loss) on sale of non-utility property											0
Interest expense:
Equity earnings of subsidiaries											48,158
Net income											48,675
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									0	0	0
Other operations									0	0	0
Maintenance									0	0	0
Depreciation and amortization									94	94	220
Income tax (benefit) expense									(960)	(498)	(398)
Property and other taxes									0	(4)	0
Total operating expenses									(866)	(408)	(178)
Net operating income									866	408	178
Other income and expenses:
Non-regulated revenue									2,333	1,985	1,850
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
Gain (loss) on sale of non-utility property									0	0	0
Income tax benefit (expense) on other income and expenses									(652)	(809)	(754)
Net other loss									1,681	1,176	1,096
Interest expense:
Interest expense									1,711	1,131	757
Allowance for borrowed funds used during construction									0	0	0
Net interest expense									1,711	1,131	757
Equity earnings of subsidiaries									64,748	72,487	48,158
Net income									65,584	72,940	48,675
Cal Water
Other income and expenses:
Gain (loss) on sale of non-utility property											(146)
Interest expense:
Equity earnings of subsidiaries											0
Net income											45,316
Cal Water | Reportable Legal Entities
Condensed Consolidating Financial Statements
Operating revenue									656,939	635,604	570,514
Operations:
Purchased water									206,675	198,682	181,018
Purchased power									22,460	21,021	19,791
Pump taxes									14,664	13,924	11,298
Administrative and general									90,563	83,163	77,247
Other operations									73,521	67,069	73,918
Maintenance									23,573	21,595	22,053
Depreciation and amortization									78,601	72,327	59,138
Income tax (benefit) expense									17,678	33,313	27,125
Property and other taxes									24,190	21,778	20,331
Total operating expenses									551,925	532,872	491,919
Net operating income									105,014	102,732	78,595
Other income and expenses:
Non-regulated revenue									17,658	14,608	15,114
Non-regulated expenses									(22,122)	(8,139)	(10,122)
Other components of net periodic benefit cost									(8,886)	(9,032)	(10,754)
Allowance for equity funds used during construction									3,954	3,750
Gain (loss) on sale of non-utility property									50	663	(146)
Income tax benefit (expense) on other income and expenses									2,616	(1,714)	2,406
Net other loss									(6,730)	136	(3,502)
Interest expense:
Interest expense									38,288	35,116	32,682
Allowance for borrowed funds used during construction									(1,909)	(2,319)	(2,905)
Net interest expense									36,379	32,797	29,777
Equity earnings of subsidiaries									0	0	0
Net income									61,905	70,071	45,316
All Other Subsidiaries
Other income and expenses:
Gain (loss) on sale of non-utility property											0
Interest expense:
Equity earnings of subsidiaries											0
Net income											2,785
All Other Subsidiaries | Reportable Legal Entities
Condensed Consolidating Financial Statements
Operating revenue									41,257	40,509	38,856
Operations:
Purchased water									428	399	497
Purchased power									8,620	7,841	7,389
Pump taxes									0	0	0
Administrative and general									10,218	10,163	10,354
Other operations									6,930	7,903	6,669
Maintenance									921	935	940
Depreciation and amortization									5,173	4,453	4,337
Income tax (benefit) expense									948	1,405	1,498
Property and other taxes									3,106	3,023	2,900
Total operating expenses									36,344	36,122	34,584
Net operating income									4,913	4,387	4,272
Other income and expenses:
Non-regulated revenue									1,197	1,814	2,006
Non-regulated expenses									(665)	(1,251)	(1,323)
Other components of net periodic benefit cost									(422)	(556)	(119)
Allowance for equity funds used during construction									0	0
Gain (loss) on sale of non-utility property									0	0	0
Income tax benefit (expense) on other income and expenses									(63)	(47)	(205)
Net other loss									47	(40)	359
Interest expense:
Interest expense									2,251	2,026	1,906
Allowance for borrowed funds used during construction									(154)	(41)	(60)
Net interest expense									2,097	1,985	1,846
Equity earnings of subsidiaries									0	0	0
Net income									$ 2,863	$ 2,362	$ 2,785