CONDENSED CONSOLIDATING FINANCIAL STATEMENTS (Details 2) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Utility plant:
Utility plant	$ 2,970,179	$ 2,717,339
Less accumulated depreciation and amortization	(922,214)	(858,062)
Net utility plant	2,047,965	1,859,277
Current assets:
Cash and cash equivalents	94,776	25,492	$ 8,837	$ 19,587
Receivables and unbilled revenue	115,454	103,023
Receivables from affiliates	0	0
Other current assets	17,643	13,554
Total current assets	227,873	142,069
Other assets:
Regulatory assets	401,147	355,930
Investments in affiliates	0	0
Long-term affiliate notes receivable	0	0
Other assets	63,390	54,469
Total other assets	464,537	410,399
TOTAL ASSETS	2,740,375	2,411,745
Capitalization:
Common stockholders' equity	693,462	659,471	642,155	626,626
Affiliate long-term debt	0	0
Long-term debt, less current maturities	515,793	531,745
Total capitalization	1,209,255	1,191,216
Current liabilities:
Current maturities of long-term debt	15,920	26,208
Short-term borrowings	275,100	97,100
Payables to affiliates	0	0
Accounts payable	93,955	77,813
Accrued expenses and other liabilities	105,984	49,109
Total current liabilities	490,959	250,230
Unamortized investment tax credits	1,724	1,798
Deferred income taxes	192,946	298,924
Pension and postretirement benefits other than pensions	252,141	222,691
Regulatory and other long-term liabilities	224,127	83,648
Advances for construction	182,502	182,448
Contributions in aid of construction	186,721	180,790
TOTAL CAPITALIZATION AND LIABILITIES	2,740,375	2,411,745
Consolidating Adjustments
Utility plant:
Utility plant	(7,196)	(7,197)
Less accumulated depreciation and amortization	2,010	1,919
Net utility plant	(5,186)	(5,278)
Current assets:
Cash and cash equivalents	0	0	0	0
Receivables and unbilled revenue	0	0
Receivables from affiliates	(24,088)	(23,182)
Other current assets	0	0
Total current assets	(24,088)	(23,182)
Other assets:
Regulatory assets	0	0
Investments in affiliates	(698,690)	(666,525)
Long-term affiliate notes receivable	(26,441)	(25,744)
Other assets	(205)	(33)
Total other assets	(725,336)	(692,302)
TOTAL ASSETS	(754,610)	(720,762)
Capitalization:
Common stockholders' equity	(703,947)	(671,836)
Affiliate long-term debt	(26,441)	(25,744)
Long-term debt, less current maturities	0	0
Total capitalization	(730,388)	(697,580)
Current liabilities:
Current maturities of long-term debt	0	0
Short-term borrowings	0	0
Payables to affiliates	(24,088)	(23,182)
Accounts payable	0	0
Accrued expenses and other liabilities	0	0
Total current liabilities	(24,088)	(23,182)
Unamortized investment tax credits	0	0
Deferred income taxes	(134)	0
Pension and postretirement benefits other than pensions	0	0
Regulatory and other long-term liabilities	0	0
Advances for construction	0	0
Contributions in aid of construction	0	0
TOTAL CAPITALIZATION AND LIABILITIES	(754,610)	(720,762)
Parent Company
Utility plant:
Utility plant	1,321	1,318
Less accumulated depreciation and amortization	(919)	(826)
Net utility plant	402	492
Current assets:
Cash and cash equivalents	4,728	5,216	582	4,108
Receivables and unbilled revenue	0	0
Receivables from affiliates	19,952	19,566
Other current assets	80	80
Total current assets	24,760	24,862
Other assets:
Regulatory assets	0	0
Investments in affiliates	698,690	666,525
Long-term affiliate notes receivable	26,441	25,744
Other assets	192	376
Total other assets	725,323	692,645
TOTAL ASSETS	750,485	717,999
Capitalization:
Common stockholders' equity	693,462	659,471
Affiliate long-term debt	0	0
Long-term debt, less current maturities	0	0
Total capitalization	693,462	659,471
Current liabilities:
Current maturities of long-term debt	0	0
Short-term borrowings	55,100	57,100
Payables to affiliates	0	0
Accounts payable	0	0
Accrued expenses and other liabilities	271	88
Total current liabilities	55,371	57,188
Unamortized investment tax credits	0	0
Deferred income taxes	1,652	1,340
Pension and postretirement benefits other than pensions	0	0
Regulatory and other long-term liabilities	0	0
Advances for construction	0	0
Contributions in aid of construction	0	0
TOTAL CAPITALIZATION AND LIABILITIES	750,485	717,999
Cal Water
Utility plant:
Utility plant	2,771,259	2,519,785
Less accumulated depreciation and amortization	(868,762)	(805,992)
Net utility plant	1,902,497	1,713,793
Current assets:
Cash and cash equivalents	80,940	13,215	4,270	13,929
Receivables and unbilled revenue	110,928	98,850
Receivables from affiliates	4,093	3,608
Other current assets	16,569	12,442
Total current assets	212,530	128,115
Other assets:
Regulatory assets	397,333	352,139
Investments in affiliates	0	0
Long-term affiliate notes receivable	0	0
Other assets	59,581	50,361
Total other assets	456,914	402,500
TOTAL ASSETS	2,571,941	2,244,408
Capitalization:
Common stockholders' equity	626,300	595,003
Affiliate long-term debt	0	0
Long-term debt, less current maturities	514,952	530,850
Total capitalization	1,141,252	1,125,853
Current liabilities:
Current maturities of long-term debt	15,598	25,657
Short-term borrowings	220,000	40,000
Payables to affiliates	580	539
Accounts payable	90,561	74,998
Accrued expenses and other liabilities	104,002	47,232
Total current liabilities	430,741	188,426
Unamortized investment tax credits	1,724	1,798
Deferred income taxes	189,004	296,781
Pension and postretirement benefits other than pensions	252,141	222,691
Regulatory and other long-term liabilities	220,779	80,518
Advances for construction	181,979	181,907
Contributions in aid of construction	154,321	146,434
TOTAL CAPITALIZATION AND LIABILITIES	2,571,941	2,244,408
All Other Subsidiaries
Utility plant:
Utility plant	204,795	203,433
Less accumulated depreciation and amortization	(54,543)	(53,163)
Net utility plant	150,252	150,270
Current assets:
Cash and cash equivalents	9,108	7,061	$ 3,985	$ 1,550
Receivables and unbilled revenue	4,526	4,173
Receivables from affiliates	43	8
Other current assets	994	1,032
Total current assets	14,671	12,274
Other assets:
Regulatory assets	3,814	3,791
Investments in affiliates	0	0
Long-term affiliate notes receivable	0	0
Other assets	3,822	3,765
Total other assets	7,636	7,556
TOTAL ASSETS	172,559	170,100
Capitalization:
Common stockholders' equity	77,647	76,833
Affiliate long-term debt	26,441	25,744
Long-term debt, less current maturities	841	895
Total capitalization	104,929	103,472
Current liabilities:
Current maturities of long-term debt	322	551
Short-term borrowings	0	0
Payables to affiliates	23,508	22,643
Accounts payable	3,394	2,815
Accrued expenses and other liabilities	1,711	1,789
Total current liabilities	28,935	27,798
Unamortized investment tax credits	0	0
Deferred income taxes	2,424	803
Pension and postretirement benefits other than pensions	0	0
Regulatory and other long-term liabilities	3,348	3,130
Advances for construction	523	541
Contributions in aid of construction	32,400	34,356
TOTAL CAPITALIZATION AND LIABILITIES	$ 172,559	$ 170,100