CONDENSED CONSOLIDATING FINANCIAL STATEMENTS (Details 5) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Operating activities:
Net income	$ 1,868	$ 20,935	$ 12,190	$ 2,719	$ 4,871	$ 20,386	$ 10,381	$ 2,018	$ 37,712	$ 37,656	$ 40,554
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation and amortization									51,981	45,265	41,643
Amortization of debt premium and expenses									1,082	979	970
Change in value of life insurance contracts									1,876	(2,641)	(4,107)
Gain on sale of non-utility property									(62)	(22)	(560)
Other changes in noncurrent assets and liabilities									5,329	3,725	3,688
Changes in operating assets and liabilities:
Other changes, net									(13,354)	(9,452)	(9,764)
Net adjustments									73,560	37,854	31,870
Net cash provided by operating activities									111,272	75,510	72,424
Investing activities:
Utility plant expenditures									(118,546)	(123,926)	(110,608)
Proceeds from sale of non-utility assets									64	34	810
Purchase of life insurance									(1,744)	(1,891)	(1,813)
Restricted cash decrease (increase)									(3,042)	3,169	(3,104)
Net cash provided by (used in) investing activites									(123,268)	(122,614)	(114,715)
Financing activities:
Short-term borrowings									23,390	85,750	20,000
Repayment of short-term borrowings										(74,000)	(48,000)
Proceeds from long-term debt, net of issuance cost									178	106,173	97,980
Retirement of long-term debt									(2,963)	(13,692)	(6,772)
Advances and contributions in aid for construction									7,231	5,313	4,981
Refunds of advances for construction									(6,205)	(6,188)	(6,039)
Dividends paid to non-affiliates									(25,674)	(24,753)	(24,476)
Issuance of common stock									965	912	614
Net cash (used in) provided by financing activities									(3,078)	79,515	38,288
Change in cash and cash equivalents									(15,074)	32,411	(4,003)
Cash and cash equivalents at beginning of year				42,277				9,866	42,277	9,866	13,869
Cash and cash equivalents at end of year	27,203				42,277				27,203	42,277	9,866
Parent Company
Operating activities:
Net income									37,712	37,656	40,554
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Equity earnings of subsidiaries									(37,222)	(36,788)	(40,303)
Dividends received from affiliates									25,674	24,753	24,476
Depreciation and amortization									51
Other changes in noncurrent assets and liabilities									(299)		(1,491)
Changes in operating assets and liabilities:
Affiliate advances										(14,579)
Other changes, net									1,882	(825)	476
Net adjustments									(9,914)	(12,860)	(16,842)
Net cash provided by operating activities									27,798	24,796	23,712
Investing activities:
Utility plant expenditures										(324)
Affiliate advances									(25,495)	(14,579)	(160)
Reduction of loans to affiliates									962	1,854	415
Net cash provided by (used in) investing activites									(24,533)	(13,049)	255
Financing activities:
Short-term borrowings									23,390	16,750
Repayment of short-term borrowings										(5,000)
Reduction of affiliate long-term borrowings									(2,045)
Dividends paid to non-affiliates									(25,674)	(24,753)	(24,476)
Issuance of common stock									965	912	614
Net cash (used in) provided by financing activities									(3,364)	(12,091)	(23,862)
Change in cash and cash equivalents									(99)	(344)	105
Cash and cash equivalents at beginning of year				188				532	188	532	427
Cash and cash equivalents at end of year	89				188				89	188	532
Cal Water
Operating activities:
Net income									38,333	35,940	38,449
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation and amortization									49,283	42,680	39,649
Amortization of debt premium and expenses									(62)		970
Change in value of life insurance contracts									1,876	(2,641)	(4,107)
Gain on sale of non-utility property									(62)	(22)	(560)
Other changes in noncurrent assets and liabilities									5,973		4,602
Changes in operating assets and liabilities:
Affiliate advances										85
Other changes, net									8,367	(9,312)	(11,161)
Net adjustments									65,437	38,140	29,393
Net cash provided by operating activities									103,770	74,080	67,842
Investing activities:
Utility plant expenditures									(98,410)	(108,990)	(100,182)
Proceeds from sale of non-utility assets									64	34	810
Affiliate advances									1,597	85	(1,039)
Reduction of loans to affiliates									45
Purchase of life insurance									(1,744)	(1,891)	(1,813)
Restricted cash decrease (increase)									(3,042)	3,169	(3,104)
Net cash provided by (used in) investing activites									(101,490)	(107,593)	(105,328)
Financing activities:
Short-term borrowings										69,000	20,000
Repayment of short-term borrowings										(69,000)	(48,000)
Proceeds from long-term debt, net of issuance cost										103,947	97,884
Retirement of long-term debt									(2,279)	(12,212)	(5,938)
Advances and contributions in aid for construction									7,082	4,962	4,981
Refunds of advances for construction									(6,129)	(6,104)	(5,968)
Dividends paid to affiliates									(22,925)	(22,634)	(22,498)
Net cash (used in) provided by financing activities									(24,251)	67,959	40,461
Change in cash and cash equivalents									(21,971)	34,446	2,975
Cash and cash equivalents at beginning of year				40,446				6,000	40,446	6,000	3,025
Cash and cash equivalents at end of year	18,475				40,446				18,475	40,446	6,000
All Other Subsidiaries
Operating activities:
Net income									(1,131)	140	1,773
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation and amortization									2,771	2,716	2,132
Other changes in noncurrent assets and liabilities									684		532
Changes in operating assets and liabilities:
Affiliate advances										14,494
Other changes, net									3,054	664	909
Net adjustments									6,509	1,247	3,573
Net cash provided by operating activities									5,378	1,387	5,346
Investing activities:
Utility plant expenditures									(20,136)	(14,612)	(10,426)
Affiliate advances											(1,199)
Reduction of loans to affiliates									2,000
Net cash provided by (used in) investing activites									(18,136)	(14,612)	(10,426)
Financing activities:
Reduction of affiliate note payable									(962)	(1,854)	(415)
Affiliate advances									23,898	14,494	1,199
Reduction of affiliate long-term borrowings									(962)
Proceeds from long-term debt, net of issuance cost									178	2,226	96
Retirement of long-term debt									(684)	(1,480)	(834)
Advances and contributions in aid for construction									149	351
Refunds of advances for construction									(76)	(84)	(71)
Dividends paid to affiliates									(2,749)	(2,119)	(1,978)
Net cash (used in) provided by financing activities									19,754	11,534	2,003
Change in cash and cash equivalents									6,996	(1,691)	(7,083)
Cash and cash equivalents at beginning of year				1,643				3,334	1,643	3,334	10,417
Cash and cash equivalents at end of year	8,639				1,643				8,639	1,643	3,334
Consolidating Adjustments
Operating activities:
Net income									(37,202)	(36,080)	(40,222)
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Equity earnings of subsidiaries									37,222	36,788	40,303
Dividends received from affiliates									(25,674)	(24,753)	(24,476)
Depreciation and amortization									(124)	(131)	(138)
Other changes in noncurrent assets and liabilities									53		45
Changes in operating assets and liabilities:
Other changes, net									51	21	12
Net adjustments									11,528	11,327	15,746
Net cash provided by operating activities									(25,674)	(24,753)	(24,476)
Investing activities:
Affiliate advances									23,898	14,494	1,199
Reduction of loans to affiliates									(3,007)	(1,854)	(415)
Net cash provided by (used in) investing activites									20,891	12,640	784
Financing activities:
Reduction of affiliate note payable									2,007	1,854	415
Affiliate advances									(23,898)	(14,494)	(1,199)
Dividends paid to affiliates									25,674	24,753	24,476
Net cash (used in) provided by financing activities									$ 4,783	$ 12,113	$ 23,692