CONDENSED CONSOLIDATING FINANCIAL STATEMENTS (Details 3) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Condensed Consolidating Financial Statements
Operating revenue	$ 121,530	$ 178,135	$ 143,552	$ 116,749	$ 103,014	$ 169,254	$ 131,397	$ 98,149	$ 559,966	$ 501,814	$ 460,399
Operations:
Purchased water									161,336	142,570	125,930
Purchased power									31,027	30,053	29,577
Pump taxes									10,336	9,130	8,600
Administrative and general									93,927	85,758	75,276
Other									77,104	54,696	56,518
Maintenance									19,142	20,698	19,685
Depreciation and amortization									54,668	50,385	42,828
Income taxes (benefits)									19,356	23,025	23,069
Taxes other than income taxes									19,227	18,332	17,103
Total operating expenses									486,123	434,647	398,586
Net operating income	11,253	36,361	19,622	6,607	7,586	30,078	19,555	9,948	73,843	67,167	61,813
Other Income and Expenses:
Non-regulated revenue									16,686	16,160	15,993
Non-regulated expense									(11,553)	(15,822)	(12,312)
Gain on sale on non-utility property									84	62	22
Income tax benefit (expense) on other income and expense									(2,096)	(141)	(1,487)
Net other income									3,121	259	2,216
Interest:
Interest expense									31,537	32,455	27,936
Less: capitalized interest									(3,401)	(2,741)	(1,563)
Net interest expense									28,136	29,714	26,373
Net income									48,828	37,712	37,656
Parent Company
Operations:
Income taxes (benefits)									(583)	(580)	(843)
Total operating expenses									(583)	(580)	(843)
Net operating income									583	580	843
Other Income and Expenses:
Non-regulated revenue									1,919	2,248	1,220
Income tax benefit (expense) on other income and expense									(782)	(916)	(497)
Net other income									1,137	1,332	723
Interest:
Interest expense									1,430	1,422	698
Net interest expense									1,430	1,422	698
Equity earnings of subsidiaries									48,538	37,222	36,788
Net income									48,828	37,712	37,656
Cal Water
Condensed Consolidating Financial Statements
Operating revenue									527,449	472,150	430,988
Operations:
Purchased water									160,913	142,355	125,749
Purchased power									21,435	20,719	21,616
Pump taxes									10,336	8,764	8,017
Administrative and general									84,399	77,622	67,536
Other									70,864	47,800	49,356
Maintenance									18,478	19,916	18,998
Depreciation and amortization									52,012	47,872	40,349
Income taxes (benefits)									18,992	23,727	23,812
Taxes other than income taxes									16,630	15,908	14,904
Total operating expenses									454,059	404,683	370,337
Net operating income									73,390	67,467	60,651
Other Income and Expenses:
Non-regulated revenue									15,204	12,972	10,064
Non-regulated expense									(9,588)	(12,287)	(7,954)
Gain on sale on non-utility property									81	62	22
Income tax benefit (expense) on other income and expense									(2,321)	(304)	(869)
Net other income									3,376	443	1,263
Interest:
Interest expense									30,328	31,421	27,059
Less: capitalized interest									(2,334)	(1,844)	(1,085)
Net interest expense									27,994	29,577	25,974
Net income									48,772	38,333	35,940
All Other Subsidiaries
Condensed Consolidating Financial Statements
Operating revenue									32,517	29,664	29,411
Operations:
Purchased water									423	215	181
Purchased power									9,592	9,334	7,961
Pump taxes										366	583
Administrative and general									9,528	8,136	7,740
Other									6,744	7,401	7,667
Maintenance									664	782	687
Depreciation and amortization									2,774	2,637	2,610
Income taxes (benefits)									(375)	(1,727)	(229)
Taxes other than income taxes									2,597	2,424	2,199
Total operating expenses									31,947	29,568	29,399
Net operating income									570	96	12
Other Income and Expenses:
Non-regulated revenue									2,420	4,322	6,670
Non-regulated expense									(1,965)	(3,535)	(4,358)
Income tax benefit (expense) on other income and expense									(266)	(422)	(1,027)
Net other income									189	365	1,285
Interest:
Interest expense									2,132	2,489	1,635
Less: capitalized interest									(1,067)	(897)	(478)
Net interest expense									1,065	1,592	1,157
Net income									(306)	(1,131)	140
Consolidating Adjustments
Operations:
Other									(504)	(505)	(505)
Depreciation and amortization									(118)	(124)	(131)
Income taxes (benefits)									1,322	1,605	329
Total operating expenses									700	976	(307)
Net operating income									(700)	(976)	307
Other Income and Expenses:
Non-regulated revenue									(2,857)	(3,382)	(1,961)
Gain on sale on non-utility property									3
Income tax benefit (expense) on other income and expense									1,273	1,501	906
Net other income									(1,581)	(1,881)	(1,055)
Interest:
Interest expense									(2,353)	(2,877)	(1,456)
Net interest expense									(2,353)	(2,877)	(1,456)
Equity earnings of subsidiaries									(48,538)	(37,222)	(36,788)
Net income									$ (48,466)	$ (37,202)	$ (36,080)