Condensed Consolidating Financial Statements (Details 2) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Utility plant:
Utility plant	$ 2,766,232	$ 2,717,339
Less accumulated depreciation and amortization	(878,227)	(858,062)
Net utility plant	1,888,005	1,859,277
Current assets:
Cash and cash equivalents	11,990	25,492	$ 30,878	$ 8,837
Receivables and unbilled revenue, net	97,043
Receivables		103,023
Receivables from affiliates	0	0
Other current assets	19,172	13,554
Total current assets	128,205	142,069
Other assets:
Regulatory assets	367,476	355,930
Investments in affiliates	0	0
Long-term affiliate notes receivable	0	0
Other assets	56,612	54,469
Total other assets	424,088	410,399
TOTAL ASSETS	2,440,298	2,411,745
Capitalization:
Common stockholders' equity	651,333	659,471
Affiliate long-term debt	0	0
Long-term debt, less current maturities	521,715	531,745
Total capitalization	1,173,048	1,191,216
Current liabilities:
Current maturities of long-term debt	36,139	26,208
Short-term borrowings	130,100	97,100
Payables to affiliates	0	0
Accounts payable	69,276	77,813
Accrued expenses and other liabilities	57,858	49,109
Total current liabilities	293,373	250,230
Unamortized investment tax credits	1,798	1,798
Deferred income taxes	299,464	298,924
Pension and postretirement benefits other than pensions	224,851	222,691
Regulatory liabilities and other	84,318	83,648
Advances for construction	182,815	182,448
Contributions in aid of construction	180,631	180,790
TOTAL CAPITALIZATION AND LIABILITIES	2,440,298	2,411,745
Consolidating Adjustments
Utility plant:
Utility plant	(7,197)	(7,197)
Less accumulated depreciation and amortization	1,942	1,919
Net utility plant	(5,255)	(5,278)
Current assets:
Cash and cash equivalents	0	0	0	0
Receivables and unbilled revenue, net	0
Receivables		0
Receivables from affiliates	(22,156)	(23,182)
Other current assets	0	0
Total current assets	(22,156)	(23,182)
Other assets:
Regulatory assets	0	0
Investments in affiliates	(658,889)	(666,525)
Long-term affiliate notes receivable	(25,393)	(25,744)
Other assets	(42)	(33)
Total other assets	(684,324)	(692,302)
TOTAL ASSETS	(711,735)	(720,762)
Capitalization:
Common stockholders' equity	(664,186)	(671,836)
Affiliate long-term debt	(25,393)	(25,744)
Long-term debt, less current maturities	0	0
Total capitalization	(689,579)	(697,580)
Current liabilities:
Current maturities of long-term debt	0	0
Short-term borrowings	0	0
Payables to affiliates	(22,156)	(23,182)
Accounts payable	0	0
Accrued expenses and other liabilities	0	0
Total current liabilities	(22,156)	(23,182)
Unamortized investment tax credits	0	0
Deferred income taxes	0	0
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	(711,735)	(720,762)
Parent Company
Utility plant:
Utility plant	1,318	1,318
Less accumulated depreciation and amortization	(849)	(826)
Net utility plant	469	492
Current assets:
Cash and cash equivalents	3,985	5,216	707	582
Receivables and unbilled revenue, net	0
Receivables		0
Receivables from affiliates	19,317	19,566
Other current assets	395	80
Total current assets	23,697	24,862
Other assets:
Regulatory assets	0	0
Investments in affiliates	658,889	666,525
Long-term affiliate notes receivable	25,393	25,744
Other assets	274	376
Total other assets	684,556	692,645
TOTAL ASSETS	708,722	717,999
Capitalization:
Common stockholders' equity	651,333	659,471
Affiliate long-term debt	0	0
Long-term debt, less current maturities	0	0
Total capitalization	651,333	659,471
Current liabilities:
Current maturities of long-term debt	0	0
Short-term borrowings	55,100	57,100
Payables to affiliates	715	0
Accounts payable	0	0
Accrued expenses and other liabilities	141	88
Total current liabilities	55,956	57,188
Unamortized investment tax credits	0	0
Deferred income taxes	1,433	1,340
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	708,722	717,999
Cal Water
Utility plant:
Utility plant	2,567,142	2,519,785
Less accumulated depreciation and amortization	(824,791)	(805,992)
Net utility plant	1,742,351	1,713,793
Current assets:
Cash and cash equivalents	2,618	13,215	26,512	4,270
Receivables and unbilled revenue, net	93,155
Receivables		98,850
Receivables from affiliates	2,653	3,608
Other current assets	17,743	12,442
Total current assets	116,169	128,115
Other assets:
Regulatory assets	363,672	352,139
Investments in affiliates	0	0
Long-term affiliate notes receivable	0	0
Other assets	52,636	50,361
Total other assets	416,308	402,500
TOTAL ASSETS	2,274,828	2,244,408
Capitalization:
Common stockholders' equity	587,853	595,003
Affiliate long-term debt	0	0
Long-term debt, less current maturities	520,815	530,850
Total capitalization	1,108,668	1,125,853
Current liabilities:
Current maturities of long-term debt	35,636	25,657
Short-term borrowings	75,000	40,000
Payables to affiliates	64	539
Accounts payable	66,254	74,998
Accrued expenses and other liabilities	55,368	47,232
Total current liabilities	232,322	188,426
Unamortized investment tax credits	1,798	1,798
Deferred income taxes	297,254	296,781
Pension and postretirement benefits other than pensions	224,851	222,691
Regulatory liabilities and other	81,129	80,518
Advances for construction	182,268	181,907
Contributions in aid of construction	146,538	146,434
TOTAL CAPITALIZATION AND LIABILITIES	2,274,828	2,244,408
All Other Subsidiaries
Utility plant:
Utility plant	204,969	203,433
Less accumulated depreciation and amortization	(54,529)	(53,163)
Net utility plant	150,440	150,270
Current assets:
Cash and cash equivalents	5,387	7,061	$ 3,659	$ 3,985
Receivables and unbilled revenue, net	3,888
Receivables		4,173
Receivables from affiliates	186	8
Other current assets	1,034	1,032
Total current assets	10,495	12,274
Other assets:
Regulatory assets	3,804	3,791
Investments in affiliates	0	0
Long-term affiliate notes receivable	0	0
Other assets	3,744	3,765
Total other assets	7,548	7,556
TOTAL ASSETS	168,483	170,100
Capitalization:
Common stockholders' equity	76,333	76,833
Affiliate long-term debt	25,393	25,744
Long-term debt, less current maturities	900	895
Total capitalization	102,626	103,472
Current liabilities:
Current maturities of long-term debt	503	551
Short-term borrowings	0	0
Payables to affiliates	21,377	22,643
Accounts payable	3,022	2,815
Accrued expenses and other liabilities	2,349	1,789
Total current liabilities	27,251	27,798
Unamortized investment tax credits	0	0
Deferred income taxes	777	803
Pension and postretirement benefits other than pensions	0	0
Regulatory liabilities and other	3,189	3,130
Advances for construction	547	541
Contributions in aid of construction	34,093	34,356
TOTAL CAPITALIZATION AND LIABILITIES	$ 168,483	$ 170,100