Condensed Consolidating Financial Statements (Details 2) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012	Dec. 31, 2011
Utility plant:
Utility plant	$ 2,160,706	$ 2,096,363
Less accumulated depreciation and amortization	(670,452)	(639,307)
Net utility plant	1,490,254	1,457,056
Current assets:
Cash and cash equivalents	38,668	38,790	20,816	27,203
Receivables, net		91,315
Receivables and unbilled revenue, net	106,138
Other current assets	19,270	16,459
Total current assets	164,076	146,564
Other assets:
Regulatory assets	353,910	344,419
Other assets	50,367	47,885
Total other assets	404,277	392,304
Total assets	2,058,607	1,995,924
Capitalization:
Common stockholders' equity	578,480	473,712
Long-term debt, less current maturities	430,705	434,467
Total capitalization	1,009,185	908,179
Current liabilities:
Current maturities of long-term debt	48,040	46,783
Short-term borrowings	28,815	89,475
Accounts payable	57,158	47,199
Accrued expenses and other liabilities	62,197	59,610
Total current liabilities	196,210	243,067
Unamortized investment tax credits	2,180	2,180
Deferred income taxes, net	167,611	158,846
Pension and postretirement benefits other than pensions	248,003	244,901
Regulatory and other liabilities	88,578	92,593
Advances for construction	186,202	187,584
Contributions in aid of construction	160,638	158,574
Total capitalization and liabilities	2,058,607	1,995,924
Parent Company
Utility plant:
Utility plant	1,079	606
Less accumulated depreciation and amortization	(136)	(108)
Net utility plant	943	498
Current assets:
Cash and cash equivalents	2,871	1,470	1,841	89
Receivables and unbilled revenue, net	76
Receivables from affiliates	26,696	19,367
Other current assets	146
Total current assets	29,789	20,837
Other assets:
Investments in affiliates	524,923	492,188
Long-term affiliate notes receivable	30,578	31,218
Other assets	1,309	1,023
Total other assets	556,810	524,429
Total assets	587,542	545,764
Capitalization:
Common stockholders' equity	578,480	473,712
Affiliate long-term debt		7,781
Total capitalization	578,480	481,493
Current liabilities:
Short-term borrowings	8,815	64,475
Payables to affiliates	820	77
Accrued expenses and other liabilities	6	298
Total current liabilities	9,641	64,850
Deferred income taxes, net	(579)	(579)
Total capitalization and liabilities	587,542	545,764
Cal Water
Utility plant:
Utility plant	1,984,718	1,927,190
Less accumulated depreciation and amortization	(636,860)	(607,992)
Net utility plant	1,347,858	1,319,198
Current assets:
Cash and cash equivalents	34,054	34,609	17,914	18,475
Receivables, net		87,482
Receivables and unbilled revenue, net	102,379
Receivables from affiliates	3,504	3,195
Other current assets	18,125	15,535
Total current assets	158,062	140,821
Other assets:
Regulatory assets	351,299	341,877
Long-term affiliate notes receivable		7,781
Other assets	42,047	40,005
Total other assets	393,346	389,663
Total assets	1,899,266	1,849,682
Capitalization:
Common stockholders' equity	478,802	442,923
Long-term debt, less current maturities	429,188	431,433
Total capitalization	907,990	874,356
Current liabilities:
Current maturities of long-term debt	46,120	46,104
Short-term borrowings	20,000	25,000
Payables to affiliates	260	1,152
Accounts payable	53,503	41,352
Accrued expenses and other liabilities	58,897	58,293
Total current liabilities	178,780	171,901
Unamortized investment tax credits	2,180	2,180
Deferred income taxes, net	164,246	155,481
Pension and postretirement benefits other than pensions	248,003	244,901
Regulatory and other liabilities	79,847	83,942
Advances for construction	185,465	186,753
Contributions in aid of construction	132,755	130,168
Total capitalization and liabilities	1,899,266	1,849,682
All Other Subsidiaries
Utility plant:
Utility plant	182,106	175,764
Less accumulated depreciation and amortization	(35,015)	(32,710)
Net utility plant	147,091	143,054
Current assets:
Cash and cash equivalents	1,743	2,711	1,061	8,639
Receivables, net		3,833
Receivables and unbilled revenue, net	3,683
Receivables from affiliates	264	1,152
Other current assets	999	924
Total current assets	6,689	8,620
Other assets:
Regulatory assets	2,611	2,542
Other assets	7,215	7,062
Total other assets	9,826	9,604
Total assets	163,606	161,278
Capitalization:
Common stockholders' equity	51,573	54,774
Affiliate long-term debt	30,578	31,218
Long-term debt, less current maturities	1,517	3,034
Total capitalization	83,668	89,026
Current liabilities:
Current maturities of long-term debt	1,920	679
Payables to affiliates	29,384	22,485
Accounts payable	3,655	5,847
Accrued expenses and other liabilities	3,294	1,019
Total current liabilities	38,253	30,030
Deferred income taxes, net	4,334	4,334
Regulatory and other liabilities	8,731	8,651
Advances for construction	737	831
Contributions in aid of construction	27,883	28,406
Total capitalization and liabilities	163,606	161,278
Consolidating Adjustments
Utility plant:
Utility plant	(7,197)	(7,197)
Less accumulated depreciation and amortization	1,559	1,503
Net utility plant	(5,638)	(5,694)
Current assets:
Receivables from affiliates	(30,464)	(23,714)
Total current assets	(30,464)	(23,714)
Other assets:
Investments in affiliates	(524,923)	(492,188)
Long-term affiliate notes receivable	(30,578)	(38,999)
Other assets	(204)	(205)
Total other assets	(555,705)	(531,392)
Total assets	(591,807)	(560,800)
Capitalization:
Common stockholders' equity	(530,375)	(497,697)
Affiliate long-term debt	(30,578)	(38,999)
Total capitalization	(560,953)	(536,696)
Current liabilities:
Payables to affiliates	(30,464)	(23,714)
Total current liabilities	(30,464)	(23,714)
Deferred income taxes, net	(390)	(390)
Total capitalization and liabilities	$ (591,807)	$ (560,800)