CONDENSED CONSOLIDATING FINANCIAL STATEMENTS (Details 2) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Utility plant:
Utility plant	$ 2,096,363	$ 1,960,381
Less accumulated depreciation and amortization	(639,307)	(579,262)
Net utility plant	1,457,056	1,381,119
Current assets:
Cash and cash equivalents	38,790	27,203	42,277	9,866
Receivables	91,315	71,588
Other current assets	16,459	15,097
Total current assets	146,564	113,888
Other assets:
Regulatory assets	344,419	319,898
Other assets	47,885	39,682
Total other assets	392,304	359,580
Total assets	1,995,924	1,854,587
Capitalization:
Common stockholders' equity	473,712	449,829	435,526	420,634
Long-term debt, less current maturities	434,467	481,632
Total capitalization	908,179	931,461
Current liabilities:
Current maturities of long-term debt	46,783	6,533
Short-term borrowings	89,475	47,140
Accounts payable	47,199	51,578
Accrued expenses and other liabilities	59,610	46,624
Total current liabilities	243,067	151,875
Unamortized investment tax credits	2,180	2,254
Deferred income taxes, net	158,846	116,368
Pension and postretirement benefits other than pensions	244,901	232,110
Regulatory and other liabilities	92,593	79,050
Advances for construction	187,584	187,278
Contributions in aid of construction	158,574	154,191
Total capitalization and liabilities	1,995,924	1,854,587
Parent Company
Utility plant:
Utility plant	606	324
Less accumulated depreciation and amortization	(108)	(51)
Net utility plant	498	273
Current assets:
Cash and cash equivalents	1,470	89	188	532
Receivables		158
Receivables from affiliates	19,367	7,817
Total current assets	20,837	8,064
Other assets:
Investments in affiliates	492,188	466,515
Long-term affiliate notes receivable	31,218	28,921
Other assets	1,023	1,144
Total other assets	524,429	496,580
Total assets	545,764	504,917
Capitalization:
Common stockholders' equity	473,712	449,829
Affiliate long-term debt	7,781	7,832
Total capitalization	481,493	457,661
Current liabilities:
Short-term borrowings	64,475	47,140
Payables to affiliates	77	52
Accrued expenses and other liabilities	298	625
Total current liabilities	64,850	47,817
Deferred income taxes, net	(579)	(561)
Total capitalization and liabilities	545,764	504,917
Cal Water
Utility plant:
Utility plant	1,927,190	1,808,568
Less accumulated depreciation and amortization	(607,992)	(551,345)
Net utility plant	1,319,198	1,257,223
Current assets:
Cash and cash equivalents	34,609	18,475	40,446	6,000
Receivables	87,482	76,227
Receivables from affiliates	3,195	3,446
Other current assets	15,535	14,225
Total current assets	140,821	112,373
Other assets:
Regulatory assets	341,877	317,564
Long-term affiliate notes receivable	7,781	7,832
Other assets	40,005	31,662
Total other assets	389,663	357,058
Total assets	1,849,682	1,726,654
Capitalization:
Common stockholders' equity	442,923	417,810
Long-term debt, less current maturities	431,433	477,998
Total capitalization	874,356	895,808
Current liabilities:
Current maturities of long-term debt	46,104	5,851
Short-term borrowings	25,000
Payables to affiliates	1,152	190
Accounts payable	41,352	47,568
Accrued expenses and other liabilities	58,293	46,462
Total current liabilities	171,901	100,071
Unamortized investment tax credits	2,180	2,254
Deferred income taxes, net	155,481	113,925
Pension and postretirement benefits other than pensions	244,901	232,110
Regulatory and other liabilities	83,942	71,034
Advances for construction	186,753	185,902
Contributions in aid of construction	130,168	125,550
Total capitalization and liabilities	1,849,682	1,726,654
All Other Subsidiaries
Utility plant:
Utility plant	175,764	158,688
Less accumulated depreciation and amortization	(32,710)	(29,251)
Net utility plant	143,054	129,437
Current assets:
Cash and cash equivalents	2,711	8,639	1,643	3,334
Receivables	3,833	(4,797)
Receivables from affiliates	1,152	5
Other current assets	924	872
Total current assets	8,620	4,719
Other assets:
Regulatory assets	2,542	2,334
Other assets	7,062	7,081
Total other assets	9,604	9,415
Total assets	161,278	143,571
Capitalization:
Common stockholders' equity	54,774	54,377
Affiliate long-term debt	31,218	28,921
Long-term debt, less current maturities	3,034	3,634
Total capitalization	89,026	86,932
Current liabilities:
Current maturities of long-term debt	679	682
Payables to affiliates	22,485	11,026
Accounts payable	5,847	4,010
Accrued expenses and other liabilities	1,019	(547)
Total current liabilities	30,030	15,171
Deferred income taxes, net	4,334	3,435
Regulatory and other liabilities	8,651	8,016
Advances for construction	831	1,376
Contributions in aid of construction	28,406	28,641
Total capitalization and liabilities	161,278	143,571
Consolidating Adjustments
Utility plant:
Utility plant	(7,197)	(7,199)
Less accumulated depreciation and amortization	1,503	1,385
Net utility plant	(5,694)	(5,814)
Current assets:
Receivables from affiliates	(23,714)	(11,268)
Total current assets	(23,714)	(11,268)
Other assets:
Investments in affiliates	(492,188)	(466,515)
Long-term affiliate notes receivable	(38,999)	(36,753)
Other assets	(205)	(205)
Total other assets	(531,392)	(503,473)
Total assets	(560,800)	(520,555)
Capitalization:
Common stockholders' equity	(497,697)	(472,187)
Affiliate long-term debt	(38,999)	(36,753)
Total capitalization	(536,696)	(508,940)
Current liabilities:
Payables to affiliates	(23,714)	(11,268)
Accrued expenses and other liabilities		84
Total current liabilities	(23,714)	(11,184)
Deferred income taxes, net	(390)	(431)
Total capitalization and liabilities	$ (560,800)	$ (520,555)