CONDENSED CONSOLIDATING FINANCIAL STATEMENTS (Details 3) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Consolidating Financial Statements
Operating revenue	$ 161,991	$ 211,731	$ 171,132	$ 122,036	$ 150,930	$ 184,268	$ 152,445	$ 121,727	$ 666,890	$ 609,370	$ 588,368
Operations:
Purchased water									199,081	181,515	168,557
Purchased power									28,862	27,180	27,890
Pump taxes									13,924	11,298	11,479
Administrative and general									102,914	98,474	113,110
Other operations									74,448	80,082	67,248
Maintenance									22,530	22,993	21,463
Depreciation and amortization									76,783	63,599	61,381
Income tax (benefit) expense									28,928	24,804	24,528
Property and other taxes									24,797	23,231	21,559
Total operating expenses									572,267	533,176	517,215
Net operating income	$ 20,118	$ 41,196	$ 25,259	$ 8,050	$ 21,335	$ 30,055	$ 18,534	$ 6,270	94,623	76,194	71,153
Other income and expenses:
Non-regulated revenue									15,898	16,585	15,624
Non-regulated expenses									(9,390)	(11,445)	(14,044)
Allowance for equity funds used during construction									3,750	0	0
Gain (loss) on sale of non-utility property									663	(146)	315
Income tax expense on other income and expenses									(4,435)	(2,012)	(761)
Net other income									6,486	2,982	1,134
Interest expense:
Interest expense									36,288	33,466	29,185
Allowance for borrowed funds used during construction									(2,360)	(2,965)	(1,915)
Net interest expense									33,928	30,501	27,270
Equity earnings of subsidiaries									0	0	0
Net income									67,181	48,675	45,017
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									(524)	(505)	(505)
Maintenance									0	0	0
Depreciation and amortization									(91)	(96)	(101)
Income tax (benefit) expense									1,059	1,010	1,008
Property and other taxes									0	0	0
Total operating expenses									444	409	402
Net operating income									(444)	(409)	(402)
Other income and expenses:
Non-regulated revenue									(2,509)	(2,385)	(2,322)
Non-regulated expenses									0	0	0
Allowance for equity funds used during construction									0
Gain (loss) on sale of non-utility property									0	0	0
Income tax expense on other income and expenses									1,022	972	967
Net other income									(1,487)	(1,413)	(1,355)
Interest expense:
Interest expense									(1,985)	(1,879)	(1,817)
Allowance for borrowed funds used during construction									0	0	0
Net interest expense									(1,985)	(1,879)	(1,817)
Equity earnings of subsidiaries									(66,728)	(48,158)	(44,516)
Net income									(66,674)	(48,101)	(44,456)
Parent Company
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	220	228
Income tax (benefit) expense									(498)	(398)	(388)
Property and other taxes									(4)	0	0
Total operating expenses									(408)	(178)	(160)
Net operating income									408	178	160
Other income and expenses:
Non-regulated revenue									1,985	1,850	1,787
Non-regulated expenses									0	0	0
Allowance for equity funds used during construction									0
Gain (loss) on sale of non-utility property									0	0	0
Income tax expense on other income and expenses									(809)	(754)	(728)
Net other income									1,176	1,096	1,059
Interest expense:
Interest expense									1,131	757	718
Allowance for borrowed funds used during construction									0	0	0
Net interest expense									1,131	757	718
Equity earnings of subsidiaries									66,728	48,158	44,516
Net income									67,181	48,675	45,017
Cal Water
Condensed Consolidating Financial Statements
Operating revenue									626,381	570,514	552,202
Operations:
Purchased water									198,682	181,018	168,157
Purchased power									21,021	19,791	20,282
Pump taxes									13,924	11,298	11,479
Administrative and general									92,195	88,001	101,244
Other operations									67,069	73,918	61,154
Maintenance									21,595	22,053	20,659
Depreciation and amortization									72,327	59,138	56,911
Income tax (benefit) expense									27,129	22,743	23,964
Property and other taxes									21,778	20,331	18,848
Total operating expenses									535,720	498,291	482,698
Net operating income									90,661	72,223	69,504
Other income and expenses:
Non-regulated revenue									14,608	15,114	14,460
Non-regulated expenses									(8,139)	(10,122)	(12,870)
Allowance for equity funds used during construction									3,750
Gain (loss) on sale of non-utility property									663	(146)	315
Income tax expense on other income and expenses									(4,434)	(1,976)	(776)
Net other income									6,448	2,870	1,129
Interest expense:
Interest expense									35,116	32,682	28,450
Allowance for borrowed funds used during construction									(2,319)	(2,905)	(1,873)
Net interest expense									32,797	29,777	26,577
Equity earnings of subsidiaries									0	0	0
Net income									64,312	45,316	44,056
All Other Subsidiaries
Condensed Consolidating Financial Statements
Operating revenue									40,509	38,856	36,166
Operations:
Purchased water									399	497	400
Purchased power									7,841	7,389	7,608
Pump taxes									0	0	0
Administrative and general									10,719	10,473	11,866
Other operations									7,903	6,669	6,599
Maintenance									935	940	804
Depreciation and amortization									4,453	4,337	4,343
Income tax (benefit) expense									1,238	1,449	(56)
Property and other taxes									3,023	2,900	2,711
Total operating expenses									36,511	34,654	34,275
Net operating income									3,998	4,202	1,891
Other income and expenses:
Non-regulated revenue									1,814	2,006	1,699
Non-regulated expenses									(1,251)	(1,323)	(1,174)
Allowance for equity funds used during construction									0
Gain (loss) on sale of non-utility property									0	0	0
Income tax expense on other income and expenses									(214)	(254)	(224)
Net other income									349	429	301
Interest expense:
Interest expense									2,026	1,906	1,834
Allowance for borrowed funds used during construction									(41)	(60)	(42)
Net interest expense									1,985	1,846	1,792
Equity earnings of subsidiaries									0	0	0
Net income									$ 2,362	$ 2,785	$ 400