Condensed Consolidating Financial Statements - Condensed Consolidating Balance Sheet (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Utility plant:
Utility plant	$ 3,169,726	$ 2,970,179
Less accumulated depreciation and amortization	(983,984)	(922,214)
Net utility plant	2,185,742	2,047,965
Current assets:
Cash and cash equivalents	66,421	94,776
Receivables and unbilled revenue	149,979	115,454
Receivables from affiliates	0	0
Other current assets	19,139	17,643
Total current assets	235,539	227,873
Other assets:
Regulatory assets	388,300	401,147
Investments in affiliates	0	0
Long-term affiliate notes receivable	0	0
Other assets	67,281	63,390
Total other assets	455,581	464,537
TOTAL ASSETS	2,876,862	2,740,375
Capitalization:
Common stockholders' equity	712,034	693,462
Affiliate long-term debt	0	0
Long-term debt, less current maturities	714,310	515,793
Total capitalization	1,426,344	1,209,255
Current liabilities:
Current maturities of long-term debt	104,812	15,920
Short-term borrowings	75,100	275,100
Payables to affiliates	0	0
Accounts payable	102,938	93,955
Accrued expenses and other liabilities	99,040	105,984
Total current liabilities	381,890	490,959
Unamortized investment tax credits	1,724	1,724
Deferred income taxes	199,143	192,946
Pension and postretirement benefits other than pensions	235,501	252,141
Regulatory liabilities and other	255,569	224,127
Advances for construction	186,897	182,502
Contributions in aid of construction	189,794	186,721
TOTAL CAPITALIZATION AND LIABILITIES	2,876,862	2,740,375
Consolidating Adjustments
Utility plant:
Utility plant	(7,196)	(7,196)
Less accumulated depreciation and amortization	2,076	2,010
Net utility plant	(5,120)	(5,186)
Current assets:
Cash and cash equivalents	0	0
Receivables and unbilled revenue	0	0
Receivables from affiliates	(45,852)	(24,088)
Other current assets	0	0
Total current assets	(45,852)	(24,088)
Other assets:
Regulatory assets	0	0
Investments in affiliates	(716,177)	(698,690)
Long-term affiliate notes receivable	(25,172)	(26,441)
Other assets	(73)	(205)
Total other assets	(741,422)	(725,336)
TOTAL ASSETS	(792,394)	(754,610)
Capitalization:
Common stockholders' equity	(721,386)	(703,947)
Affiliate long-term debt	0	(26,441)
Long-term debt, less current maturities	(25,172)	0
Total capitalization	(746,558)	(730,388)
Current liabilities:
Current maturities of long-term debt	0	0
Short-term borrowings	0	0
Payables to affiliates	(45,852)	(24,088)
Accounts payable	0	0
Accrued expenses and other liabilities	0	0
Total current liabilities	(45,852)	(24,088)
Unamortized investment tax credits	0	0
Deferred income taxes	0	(134)
Pension and postretirement benefits other than pensions	0	0
Regulatory liabilities and other	16	0
Advances for construction	0	0
Contributions in aid of construction	0	0
TOTAL CAPITALIZATION AND LIABILITIES	(792,394)	(754,610)
Parent Company | Reportable Legal Entities
Utility plant:
Utility plant	1,317	1,321
Less accumulated depreciation and amortization	(989)	(919)
Net utility plant	328	402
Current assets:
Cash and cash equivalents	2,445	4,728
Receivables and unbilled revenue	0	0
Receivables from affiliates	44,671	19,952
Other current assets	203	80
Total current assets	47,319	24,760
Other assets:
Regulatory assets	0	0
Investments in affiliates	716,177	698,690
Long-term affiliate notes receivable	25,172	26,441
Other assets	70	192
Total other assets	741,419	725,323
TOTAL ASSETS	789,066	750,485
Capitalization:
Common stockholders' equity	712,034	693,462
Affiliate long-term debt	0	0
Long-term debt, less current maturities	0	0
Total capitalization	712,034	693,462
Current liabilities:
Current maturities of long-term debt	0	0
Short-term borrowings	75,100	55,100
Payables to affiliates	0	0
Accounts payable	0	0
Accrued expenses and other liabilities	112	271
Total current liabilities	75,212	55,371
Unamortized investment tax credits	0	0
Deferred income taxes	1,820	1,652
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	789,066	750,485
Cal Water | Reportable Legal Entities
Utility plant:
Utility plant	2,963,674	2,771,259
Less accumulated depreciation and amortization	(926,291)	(868,762)
Net utility plant	2,037,383	1,902,497
Current assets:
Cash and cash equivalents	55,108	80,940
Receivables and unbilled revenue	144,340	110,928
Receivables from affiliates	895	4,093
Other current assets	17,360	16,569
Total current assets	217,703	212,530
Other assets:
Regulatory assets	384,249	397,333
Investments in affiliates	0	0
Long-term affiliate notes receivable	0	0
Other assets	63,624	59,581
Total other assets	447,873	456,914
TOTAL ASSETS	2,702,959	2,571,941
Capitalization:
Common stockholders' equity	642,588	626,300
Affiliate long-term debt	0	0
Long-term debt, less current maturities	713,622	514,952
Total capitalization	1,356,210	1,141,252
Current liabilities:
Current maturities of long-term debt	104,538	15,598
Short-term borrowings	0	220,000
Payables to affiliates	21,710	580
Accounts payable	99,315	90,561
Accrued expenses and other liabilities	94,675	104,002
Total current liabilities	320,238	430,741
Unamortized investment tax credits	1,724	1,724
Deferred income taxes	193,864	189,004
Pension and postretirement benefits other than pensions	235,501	252,141
Regulatory liabilities and other	251,235	220,779
Advances for construction	186,389	181,979
Contributions in aid of construction	157,798	154,321
TOTAL CAPITALIZATION AND LIABILITIES	2,702,959	2,571,941
All Other Subsidiaries | Reportable Legal Entities
Utility plant:
Utility plant	211,931	204,795
Less accumulated depreciation and amortization	(58,780)	(54,543)
Net utility plant	153,151	150,252
Current assets:
Cash and cash equivalents	8,868	9,108
Receivables and unbilled revenue	5,639	4,526
Receivables from affiliates	286	43
Other current assets	1,576	994
Total current assets	16,369	14,671
Other assets:
Regulatory assets	4,051	3,814
Investments in affiliates	0	0
Long-term affiliate notes receivable	0	0
Other assets	3,660	3,822
Total other assets	7,711	7,636
TOTAL ASSETS	177,231	172,559
Capitalization:
Common stockholders' equity	78,798	77,647
Affiliate long-term debt	0	26,441
Long-term debt, less current maturities	25,860	841
Total capitalization	104,658	104,929
Current liabilities:
Current maturities of long-term debt	274	322
Short-term borrowings	0	0
Payables to affiliates	24,142	23,508
Accounts payable	3,623	3,394
Accrued expenses and other liabilities	4,253	1,711
Total current liabilities	32,292	28,935
Unamortized investment tax credits	0	0
Deferred income taxes	3,459	2,424
Pension and postretirement benefits other than pensions	0	0
Regulatory liabilities and other	4,318	3,348
Advances for construction	508	523
Contributions in aid of construction	31,996	32,400
TOTAL CAPITALIZATION AND LIABILITIES	$ 177,231	$ 172,559