Condensed Consolidating Financial Statements (Details3) (USD $) In Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Operating activities:
Net income (loss)	$ 12,190	$ 10,381	$ 14,909	$ 12,399
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation and amortization			25,837	22,857
Change in value of life insurance contracts			(40)	83
Gain on sale of non-utility assets	(62)		(62)
Other changes in noncurrent assets and liabilities			8,625	(1,008)
Changes in operating assets and liabilities:
Other changes, net			(1,602)	(1,475)
Net adjustments			32,758	20,457
Net cash provided by operating activities			47,667	32,856
Investing activities:
Utility plant expenditures			(52,268)	(60,458)
Purchase of life insurance			(1,658)	(1,706)
Restricted cash decrease			(220)	(13)
Proceeds from sale of non-utility assets			63
Net cash used in investing activities			(54,083)	(62,177)
Financing Activities:
Short-term borrowings, net			9,010	43,150
Proceeds from long-term debt			110	7,903
Repayment of long-term borrowings			(1,326)	(12,187)
Advances and contributions in aid for construction			5,061	1,620
Refunds of advances for construction			(3,008)	(3,018)
Dividends paid to non-affiliates			(12,826)	(12,367)
Net cash (used in) provided by financing activities			(2,979)	25,101
Change in cash and cash equivalents			(9,395)	(4,220)
Cash and cash equivalents at beginning of period			42,277	9,866
Cash and cash equivalents at end of period	32,882	5,646	32,882	5,646
California Water Service Group
Operating activities:
Net income (loss)	12,190	10,381	14,909	12,399
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Equity earnings of subsidiaries	(12,060)	(10,312)	(14,689)	(12,224)
Dividends received from affiliates			12,826	12,367
Depreciation and amortization			23
Changes in operating assets and liabilities:
Net (decrease) increase in advances to affiliates			(9,959)	(10,159)
Other changes, net			864	(229)
Net adjustments			(10,935)	(10,245)
Net cash provided by operating activities			3,974	2,154
Investing activities:
Proceeds from affiliate long-term debt			515	1,531
Net cash used in investing activities			515	1,531
Financing Activities:
Short-term borrowings, net			9,010	8,150
Repayment of affiliate long-term borrowings			(58)
Dividends paid to non-affiliates			(12,826)	(12,367)
Net cash (used in) provided by financing activities			(3,874)	(4,217)
Change in cash and cash equivalents			615	(532)
Cash and cash equivalents at beginning of period			188	532
Cash and cash equivalents at end of period	803		803
Cal Water
Operating activities:
Net income (loss)	12,187	10,325	15,232	12,534
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation and amortization			24,475	21,619
Change in value of life insurance contracts			(40)	83
Gain on sale of non-utility assets	(62)		(62)
Other changes in noncurrent assets and liabilities			8,084	(753)
Changes in operating assets and liabilities:
Net (decrease) increase in advances to affiliates			3,620	1,761
Other changes, net			(2,477)	(3,127)
Net adjustments			33,600	19,583
Net cash provided by operating activities			48,832	32,117
Investing activities:
Utility plant expenditures			(46,233)	(50,686)
Purchase of life insurance			(1,658)	(1,706)
Restricted cash decrease			(220)	(13)
Proceeds from affiliate long-term debt			22
Proceeds from sale of non-utility assets			63
Net cash used in investing activities			(48,026)	(52,405)
Financing Activities:
Short-term borrowings, net				35,000
Proceeds from long-term debt				5,805
Repayment of long-term borrowings			(1,007)	(11,083)
Advances and contributions in aid for construction			4,441	1,563
Refunds of advances for construction			(2,999)	(2,999)
Dividends paid to affiliates			(11,451)	(11,329)
Net cash (used in) provided by financing activities			(11,016)	16,957
Change in cash and cash equivalents			(10,210)	(3,331)
Cash and cash equivalents at beginning of period			40,446	6,000
Cash and cash equivalents at end of period	30,236	2,669	30,236	2,669
All Other Subsidiaries
Operating activities:
Net income (loss)	(145)	4	(580)	(349)
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation and amortization			1,401	1,303
Other changes in noncurrent assets and liabilities			541	(255)
Changes in operating assets and liabilities:
Net (decrease) increase in advances to affiliates			6,339	8,398
Other changes, net			(14)	1,855
Net adjustments			8,267	11,301
Net cash provided by operating activities			7,687	10,952
Investing activities:
Utility plant expenditures			(6,035)	(9,772)
Proceeds from affiliate long-term debt			36
Net cash used in investing activities			(5,999)	(9,772)
Financing Activities:
Repayment of affiliate long-term borrowings			(515)	(1,531)
Proceeds from long-term debt			110	2,098
Repayment of long-term borrowings			(319)	(1,104)
Advances and contributions in aid for construction			620	57
Refunds of advances for construction			(9)	(19)
Dividends paid to affiliates			(1,375)	(1,038)
Net cash (used in) provided by financing activities			(1,488)	(1,537)
Change in cash and cash equivalents			200	(357)
Cash and cash equivalents at beginning of period			1,643	3,334
Cash and cash equivalents at end of period	1,843	2,977	1,843	2,977
Consolidating Adjustments
Operating activities:
Net income (loss)	(12,042)	(10,329)	(14,652)	(12,185)
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Equity earnings of subsidiaries	12,060	10,312	14,689	12,224
Dividends received from affiliates			(12,826)	(12,367)
Depreciation and amortization			(62)	(65)
Changes in operating assets and liabilities:
Other changes, net			25	26
Net adjustments			1,826	(182)
Net cash provided by operating activities			(12,826)	(12,367)
Investing activities:
Proceeds from affiliate long-term debt			(573)	(1,531)
Net cash used in investing activities			(573)	(1,531)
Financing Activities:
Repayment of affiliate long-term borrowings			573	1,531
Dividends paid to affiliates			12,826	12,367
Net cash (used in) provided by financing activities			$ 13,399	$ 13,898