Condensed Consolidating Financial Statements (Details) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2010	Dec. 31, 2009
Utility plant:
Utility plant	$ 1,895,384	$ 1,843,766
Less accumulated depreciation and amortization	(567,788)	(549,469)
Net utility plant	1,327,596	1,294,297
Current assets:
Cash and cash equivalents	32,882	42,277	5,646	9,866
Receivables and unbilled revenue	71,398	59,908
Other current assets	27,331	24,025
Total current assets	131,611	126,210
Other assets:
Regulatory assets	245,956	229,577
Other assets	37,375	39,367
Total other assets	285,946	271,559
Total assets	1,745,153	1,692,066
Capitalization:
Common stockholders' equity	438,240	435,526
Long-term debt, less current maturities	477,968	479,181
Total capitalization	916,208	914,707
Current liabilities:
Current maturities of long-term debt	2,377	2,380
Short-term borrowings	32,760	23,750
Accounts payable	51,647	39,505
Accrued expenses and other liabilities	42,545	38,688
Total current liabilities	131,626	107,348
Unamortized investment tax credits	2,244	2,244
Deferred income taxes, net	120,046	107,084
Pension and postretirement benefits other than pensions	162,439	155,224
Regulatory and other liabilities	70,726	82,204
Advances for construction	187,277	186,899
Contributions in aid of construction	154,587	136,356
Total capitalization and liabilities	1,745,153	1,692,066
California Water Service Group
Utility plant:
Utility plant	324	324
Less accumulated depreciation and amortization	(23)
Net utility plant	301	324
Current assets:
Cash and cash equivalents	803	188		532
Receivables and unbilled revenue	182
Receivables from affiliates	14,676	3,478
Other current assets	123	181
Total current assets	15,784	3,847
Other assets:
Investments in affiliates	436,185	434,322
Long-term affiliate notes receivable	31,871	34,517
Other assets	848	848
Total other assets	468,904	469,687
Total assets	484,989	473,858
Capitalization:
Common stockholders' equity	438,240	435,527
Affiliate long-term debt	9,747	9,808
Total capitalization	447,987	445,335
Current liabilities:
Short-term borrowings	32,760	23,750
Payables to affiliates	4,377	5,265
Accrued expenses and other liabilities	424	67
Total current liabilities	37,561	29,082
Deferred income taxes, net	(559)	(559)
Total capitalization and liabilities	484,989	473,858
Cal Water
Utility plant:
Utility plant	1,757,453	1,710,213
Less accumulated depreciation and amortization	(540,388)	(522,486)
Net utility plant	1,217,065	1,187,727
Current assets:
Cash and cash equivalents	30,236	40,446	2,669	6,000
Receivables and unbilled revenue	67,479	56,068
Receivables from affiliates	1,433	4,907
Other current assets	25,992	22,842
Total current assets	125,140	124,263
Other assets:
Regulatory assets	243,750	227,440
Long-term affiliate notes receivable	7,856	7,880
Other assets	32,363	34,153
Total other assets	283,969	269,473
Total assets	1,626,174	1,581,463
Capitalization:
Common stockholders' equity	406,183	402,402
Long-term debt, less current maturities	474,023	475,030
Total capitalization	880,206	877,432
Current liabilities:
Current maturities of long-term debt	1,709	1,709
Payables to affiliates	201	56
Accounts payable	50,838	38,204
Accrued expenses and other liabilities	36,480	34,444
Total current liabilities	89,228	74,413
Unamortized investment tax credits	2,244	2,244
Deferred income taxes, net	118,749	105,786
Pension and postretirement benefits other than pensions	162,439	155,224
Regulatory and other liabilities	62,093	74,057
Advances for construction	185,834	185,332
Contributions in aid of construction	125,381	106,975
Total capitalization and liabilities	1,626,174	1,581,463
All Other Subsidiaries
Utility plant:
Utility plant	144,806	140,428
Less accumulated depreciation and amortization	(28,700)	(28,244)
Net utility plant	116,106	112,184
Current assets:
Cash and cash equivalents	1,843	1,643	2,977	3,334
Receivables and unbilled revenue	3,737	3,840
Receivables from affiliates	3,524	3,621
Other current assets	1,216	1,002
Total current assets	10,320	10,106
Other assets:
Regulatory assets	2,206	2,137
Long-term affiliate notes receivable	1,891	1,928
Other assets	6,984	7,186
Total other assets	11,081	11,251
Total assets	137,507	133,541
Capitalization:
Common stockholders' equity	35,658	37,611
Affiliate long-term debt	31,871	34,517
Long-term debt, less current maturities	3,945	4,151
Total capitalization	71,474	76,279
Current liabilities:
Current maturities of long-term debt	668	671
Payables to affiliates	15,055	6,685
Accounts payable	3,106	4,326
Accrued expenses and other liabilities	5,583	4,145
Total current liabilities	24,412	15,827
Deferred income taxes, net	2,339	2,340
Regulatory and other liabilities	8,663	8,147
Advances for construction	1,443	1,567
Contributions in aid of construction	29,206	29,381
Total capitalization and liabilities	137,507	133,541
Consolidating Adjustments
Utility plant:
Utility plant	(7,199)	(7,199)
Less accumulated depreciation and amortization	1,323	1,261
Net utility plant	(5,876)	(5,938)
Current assets:
Receivables from affiliates	(19,633)	(12,006)
Total current assets	(19,633)	(12,006)
Other assets:
Investments in affiliates	(436,185)	(434,322)
Long-term affiliate notes receivable	(41,618)	(44,325)
Other assets	(205)	(205)
Total other assets	(478,008)	(478,852)
Total assets	(503,517)	(496,796)
Capitalization:
Common stockholders' equity	(441,841)	(440,014)
Affiliate long-term debt	(41,618)	(44,325)
Total capitalization	(483,459)	(484,339)
Current liabilities:
Payables to affiliates	(19,633)	(12,006)
Accrued expenses and other liabilities	58	32
Total current liabilities	(19,575)	(11,974)
Deferred income taxes, net	(483)	(483)
Total capitalization and liabilities	$ (503,517)	$ (496,796)