Condensed Consolidating Financial Statements (Details 2) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2011
Utility plant:
Utility plant	$ 2,190,573	$ 2,096,363
Less accumulated depreciation and amortization	(685,351)	(639,307)
Net utility plant	1,505,222	1,457,056
Current assets:
Cash and cash equivalents	48,847	38,790	16,971	27,203
Receivables and unbilled revenue, net	105,643	91,315
Other current assets	16,062	16,459
Total current assets	170,552	146,564
Other assets:
Regulatory assets	354,879	344,419
Other assets	52,780	47,885
Total other assets	407,659	392,304
Total assets	2,083,433	1,995,924
Capitalization:
Common stockholders' equity	600,254	473,712
Long-term debt, less current maturities	430,227	434,467
Total capitalization	1,030,481	908,179
Current liabilities:
Current maturities of long-term debt	48,013	46,783
Short-term borrowings	11,515	89,475
Accounts payable	60,414	47,199
Accrued expenses and other liabilities	77,071	59,610
Total current liabilities	197,013	243,067
Unamortized investment tax credits	2,180	2,180
Deferred income taxes, net	168,091	158,846
Pension and postretirement benefits other than pensions	247,335	244,901
Regulatory and other liabilities	91,185	92,593
Advances for construction	184,879	187,584
Contributions in aid of construction	162,269	158,574
Total capitalization and liabilities	2,083,433	1,995,924
Parent Company
Utility plant:
Utility plant	1,246	606
Less accumulated depreciation and amortization	(150)	(108)
Net utility plant	1,096	498
Current assets:
Cash and cash equivalents	4,272	1,470	1,198	89
Receivables from affiliates	28,964	19,367
Other current assets	73
Total current assets	33,309	20,837
Other assets:
Investments in affiliates	546,123	492,188
Long-term affiliate notes receivable	30,252	31,218
Other assets	1,196	1,023
Total other assets	577,571	524,429
Total assets	611,976	545,764
Capitalization:
Common stockholders' equity	600,254	473,712
Affiliate long-term debt		7,781
Total capitalization	600,254	481,493
Current liabilities:
Short-term borrowings	11,515	64,475
Payables to affiliates	24	77
Accrued expenses and other liabilities	762	298
Total current liabilities	12,301	64,850
Deferred income taxes, net	(579)	(579)
Total capitalization and liabilities	611,976	545,764
Cal Water
Utility plant:
Utility plant	2,013,475	1,927,190
Less accumulated depreciation and amortization	(650,679)	(607,992)
Net utility plant	1,362,796	1,319,198
Current assets:
Cash and cash equivalents	42,545	34,609	14,439	18,475
Receivables and unbilled revenue, net	100,810	87,482
Receivables from affiliates	5,539	3,195
Other current assets	15,038	15,535
Total current assets	163,932	140,821
Other assets:
Regulatory assets	352,232	341,877
Long-term affiliate notes receivable		7,781
Other assets	44,610	40,005
Total other assets	396,842	389,663
Total assets	1,923,570	1,849,682
Capitalization:
Common stockholders' equity	500,359	442,923
Long-term debt, less current maturities	428,878	431,433
Total capitalization	929,237	874,356
Current liabilities:
Current maturities of long-term debt	46,129	46,104
Short-term borrowings		25,000
Payables to affiliates	180	1,152
Accounts payable	57,434	41,352
Accrued expenses and other liabilities	75,168	58,293
Total current liabilities	178,911	171,901
Unamortized investment tax credits	2,180	2,180
Deferred income taxes, net	164,716	155,481
Pension and postretirement benefits other than pensions	247,335	244,901
Regulatory and other liabilities	82,416	83,942
Advances for construction	184,110	186,753
Contributions in aid of construction	134,665	130,168
Total capitalization and liabilities	1,923,570	1,849,682
All Other Subsidiaries
Utility plant:
Utility plant	183,049	175,764
Less accumulated depreciation and amortization	(36,109)	(32,710)
Net utility plant	146,940	143,054
Current assets:
Cash and cash equivalents	2,030	2,711	1,334	8,639
Receivables and unbilled revenue, net	4,833	3,833
Receivables from affiliates	181	1,152
Other current assets	951	924
Total current assets	7,995	8,620
Other assets:
Regulatory assets	2,647	2,542
Other assets	7,179	7,062
Total other assets	9,826	9,604
Total assets	164,761	161,278
Capitalization:
Common stockholders' equity	51,271	54,774
Affiliate long-term debt	30,252	31,218
Long-term debt, less current maturities	1,349	3,034
Total capitalization	82,872	89,026
Current liabilities:
Current maturities of long-term debt	1,884	679
Payables to affiliates	34,480	22,485
Accounts payable	2,980	5,847
Accrued expenses and other liabilities	1,059	1,019
Total current liabilities	40,403	30,030
Deferred income taxes, net	4,344	4,334
Regulatory and other liabilities	8,769	8,651
Advances for construction	769	831
Contributions in aid of construction	27,604	28,406
Total capitalization and liabilities	164,761	161,278
Consolidating Adjustments
Utility plant:
Utility plant	(7,197)	(7,197)
Less accumulated depreciation and amortization	1,587	1,503
Net utility plant	(5,610)	(5,694)
Current assets:
Receivables from affiliates	(34,684)	(23,714)
Total current assets	(34,684)	(23,714)
Other assets:
Investments in affiliates	(546,123)	(492,188)
Long-term affiliate notes receivable	(30,252)	(38,999)
Other assets	(205)	(205)
Total other assets	(576,580)	(531,392)
Total assets	(616,874)	(560,800)
Capitalization:
Common stockholders' equity	(551,630)	(497,697)
Affiliate long-term debt	(30,252)	(38,999)
Total capitalization	(581,882)	(536,696)
Current liabilities:
Payables to affiliates	(34,684)	(23,714)
Accrued expenses and other liabilities	82
Total current liabilities	(34,602)	(23,714)
Deferred income taxes, net	(390)	(390)
Total capitalization and liabilities	$ (616,874)	$ (560,800)