Condensed Consolidating Financial Statements (Details 2) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Utility plant:
Utility plant	$ 2,560,787	$ 2,506,946
Less accumulated depreciation and amortization	(821,108)	(805,178)
Net utility plant	1,739,679	1,701,768
Current assets:
Cash and cash equivalents	30,878	8,837	$ 33,311	$ 19,587
Receivables and unbilled revenue	101,214	104,505
Receivables from affiliates	0	0
Other current assets	16,429	14,236
Total current assets	148,521	127,578
Other assets:
Regulatory assets	361,249	361,893
Investments in affiliates	0	0
Long-term affiliate notes receivable	0	0
Other assets	50,356	50,014
Total other assets	411,605	411,907
TOTAL ASSETS	2,299,805	2,241,253
Capitalization:
Common stockholders’ equity	632,967	642,155
Affiliate long-term debt	0	0
Long-term debt, less current maturities	557,849	508,002
Total capitalization	1,190,816	1,150,157
Current liabilities:
Current maturities of long-term debt	6,113	6,043
Short-term borrowings	34,500	33,615
Payables to affiliates	0	0
Accounts payable	65,354	66,380
Accrued expenses and other liabilities	52,176	41,860
Total current liabilities	158,143	147,898
Unamortized investment tax credits	1,872	1,872
Deferred income taxes	264,153	264,897
Pension and postretirement benefits other than pensions	239,164	236,266
Regulatory liabilities and other	88,018	82,414
Advances for construction	180,210	180,172
Contributions in aid of construction	177,429	177,577
TOTAL CAPITALIZATION AND LIABILITIES	2,299,805	2,241,253
Consolidating Adjustments
Utility plant:
Utility plant	(7,197)	(7,197)
Less accumulated depreciation and amortization	1,847	1,823
Net utility plant	(5,350)	(5,374)
Current assets:
Cash and cash equivalents	0	0	0	0
Receivables and unbilled revenue	0	0
Receivables from affiliates	(43,831)	(45,896)
Other current assets	0	0
Total current assets	(43,831)	(45,896)
Other assets:
Regulatory assets	0	0
Investments in affiliates	(642,254)	(651,449)
Long-term affiliate notes receivable	(24,806)	(25,099)
Other assets	(916)	(904)
Total other assets	(667,976)	(677,452)
TOTAL ASSETS	(717,157)	(728,722)
Capitalization:
Common stockholders’ equity	(647,607)	(656,816)
Affiliate long-term debt	(24,806)	(25,099)
Long-term debt, less current maturities	0	0
Total capitalization	(672,413)	(681,915)
Current liabilities:
Current maturities of long-term debt	0	0
Short-term borrowings	0	0
Payables to affiliates	(43,831)	(45,896)
Accounts payable	0	0
Accrued expenses and other liabilities	0	0
Total current liabilities	(43,831)	(45,896)
Unamortized investment tax credits	0	0
Deferred income taxes	(913)	(911)
Pension and postretirement benefits other than pensions	0	0
Regulatory liabilities and other	0	0
Advances for construction	0	0
Contributions in aid of construction	0	0
TOTAL CAPITALIZATION AND LIABILITIES	(717,157)	(728,722)
Parent Company
Utility plant:
Utility plant	1,318	1,318
Less accumulated depreciation and amortization	(662)	(605)
Net utility plant	656	713
Current assets:
Cash and cash equivalents	707	582	316	4,108
Receivables and unbilled revenue	0	0
Receivables from affiliates	19,902	19,677
Other current assets	367	79
Total current assets	20,976	20,338
Other assets:
Regulatory assets	0	0
Investments in affiliates	642,254	651,449
Long-term affiliate notes receivable	24,806	25,099
Other assets	564	758
Total other assets	667,624	677,306
TOTAL ASSETS	689,256	698,357
Capitalization:
Common stockholders’ equity	632,967	642,155
Affiliate long-term debt	0	0
Long-term debt, less current maturities	0	0
Total capitalization	632,967	642,155
Current liabilities:
Current maturities of long-term debt	0	0
Short-term borrowings	34,500	33,615
Payables to affiliates	20,600	21,500
Accounts payable	0	0
Accrued expenses and other liabilities	109	102
Total current liabilities	55,209	55,217
Unamortized investment tax credits	0	0
Deferred income taxes	1,080	985
Pension and postretirement benefits other than pensions	0	0
Regulatory liabilities and other	0	0
Advances for construction	0	0
Contributions in aid of construction	0	0
TOTAL CAPITALIZATION AND LIABILITIES	689,256	698,357
Cal Water
Utility plant:
Utility plant	2,366,430	2,313,704
Less accumulated depreciation and amortization	(772,988)	(758,362)
Net utility plant	1,593,442	1,555,342
Current assets:
Cash and cash equivalents	26,512	4,270	31,200	13,929
Receivables and unbilled revenue	97,211	100,777
Receivables from affiliates	23,851	26,219
Other current assets	15,004	13,077
Total current assets	162,578	144,343
Other assets:
Regulatory assets	357,586	358,254
Investments in affiliates	0	0
Long-term affiliate notes receivable	0	0
Other assets	46,009	45,544
Total other assets	403,595	403,798
TOTAL ASSETS	2,159,615	2,103,483
Capitalization:
Common stockholders’ equity	572,846	581,792
Affiliate long-term debt	0	0
Long-term debt, less current maturities	556,813	507,034
Total capitalization	1,129,659	1,088,826
Current liabilities:
Current maturities of long-term debt	5,655	5,654
Short-term borrowings	0	0
Payables to affiliates	568	667
Accounts payable	62,276	63,814
Accrued expenses and other liabilities	49,313	40,173
Total current liabilities	117,812	110,308
Unamortized investment tax credits	1,872	1,872
Deferred income taxes	263,986	264,823
Pension and postretirement benefits other than pensions	239,164	236,266
Regulatory liabilities and other	85,035	79,477
Advances for construction	179,653	179,630
Contributions in aid of construction	142,434	142,281
TOTAL CAPITALIZATION AND LIABILITIES	2,159,615	2,103,483
All Other Subsidiaries
Utility plant:
Utility plant	200,236	199,121
Less accumulated depreciation and amortization	(49,305)	(48,034)
Net utility plant	150,931	151,087
Current assets:
Cash and cash equivalents	3,659	3,985	$ 1,795	$ 1,550
Receivables and unbilled revenue	4,003	3,728
Receivables from affiliates	78	0
Other current assets	1,058	1,080
Total current assets	8,798	8,793
Other assets:
Regulatory assets	3,663	3,639
Investments in affiliates	0	0
Long-term affiliate notes receivable	0	0
Other assets	4,699	4,616
Total other assets	8,362	8,255
TOTAL ASSETS	168,091	168,135
Capitalization:
Common stockholders’ equity	74,761	75,024
Affiliate long-term debt	24,806	25,099
Long-term debt, less current maturities	1,036	968
Total capitalization	100,603	101,091
Current liabilities:
Current maturities of long-term debt	458	389
Short-term borrowings	0	0
Payables to affiliates	22,663	23,729
Accounts payable	3,078	2,566
Accrued expenses and other liabilities	2,754	1,585
Total current liabilities	28,953	28,269
Unamortized investment tax credits	0	0
Deferred income taxes	0	0
Pension and postretirement benefits other than pensions	0	0
Regulatory liabilities and other	2,983	2,937
Advances for construction	557	542
Contributions in aid of construction	34,995	35,296
TOTAL CAPITALIZATION AND LIABILITIES	$ 168,091	$ 168,135