Condensed Consolidating Financial Statements - Condensed Consolidating Balance Sheet (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Utility plant:
Utility plant	$ 3,752,243		$ 3,550,485
Less accumulated depreciation and amortization	(1,214,427)		(1,144,115)
Net utility plant	2,537,816		2,406,370
Current assets:
Cash and cash equivalents	114,388		42,653
Receivables and unbilled revenue, net	123,029		119,349
Receivables from affiliates	0		0
Other current assets	29,472		22,710
Total current assets	266,889		184,712
Other assets:
Regulatory assets	440,986		433,322
Investments in affiliates	0		0
Long-term affiliate notes receivable	0		0
Other assets	114,242		86,904
Total other assets	555,228		520,226
TOTAL ASSETS	3,359,933		3,111,308
Capitalization:
Common stockholders’ equity	782,023	$ 755,140	779,906	$ 723,164	$ 714,129	$ 730,157
Affiliate long-term debt	0		0
Long-term debt, net	785,257		786,754
Total capitalization	1,567,280		1,566,660
Current liabilities:
Current maturities of long-term debt, net	21,872		21,868
Short-term borrowings	375,100		175,100
Payables to affiliates	0		0
Accounts payable	128,216		108,463
Accrued expenses and other liabilities	52,364		53,290
Total current liabilities	577,552		358,721
Deferred income taxes	223,955		222,590
Pension and postretirement benefits other than pensions	261,119		258,907
Regulatory liabilities and other	270,177		271,831
Advances for construction	195,056		191,062
Contributions in aid of construction	264,794		241,537
TOTAL CAPITALIZATION AND LIABILITIES	3,359,933		3,111,308
Consolidating Adjustments
Utility plant:
Utility plant	(7,197)		(7,197)
Less accumulated depreciation and amortization	2,219		2,180
Net utility plant	(4,978)		(5,017)
Current assets:
Cash and cash equivalents	0		0
Receivables and unbilled revenue, net	0		0
Receivables from affiliates	(24,365)		(29,633)
Other current assets	0		0
Total current assets	(24,365)		(29,633)
Other assets:
Regulatory assets	0		0
Investments in affiliates	(811,993)		(777,170)
Long-term affiliate notes receivable	(33,160)		(30,060)
Other assets	(220)		(221)
Total other assets	(845,373)		(807,451)
TOTAL ASSETS	(874,716)		(842,101)
Capitalization:
Common stockholders’ equity	(817,182)		(782,388)
Affiliate long-term debt	(33,160)		(30,060)
Long-term debt, net	0		0
Total capitalization	(850,342)		(812,448)
Current liabilities:
Current maturities of long-term debt, net	0		0
Short-term borrowings	0		0
Payables to affiliates	(24,365)		(29,633)
Accounts payable	0		0
Accrued expenses and other liabilities	0		0
Total current liabilities	(24,365)		(29,633)
Deferred income taxes	(9)		(20)
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	(874,716)		(842,101)
Parent Company | Reportable Legal Entities
Utility plant:
Utility plant	1,318		1,318
Less accumulated depreciation and amortization	(1,154)		(1,107)
Net utility plant	164		211
Current assets:
Cash and cash equivalents	19,229		3,096
Receivables and unbilled revenue, net	0		0
Receivables from affiliates	23,391		25,803
Other current assets	453		90
Total current assets	43,073		28,989
Other assets:
Regulatory assets	0		0
Investments in affiliates	811,993		777,170
Long-term affiliate notes receivable	33,160		30,060
Other assets	422		409
Total other assets	845,575		807,639
TOTAL ASSETS	888,812		836,839
Capitalization:
Common stockholders’ equity	782,023		779,906
Affiliate long-term debt	0		0
Long-term debt, net	0		0
Total capitalization	782,023		779,906
Current liabilities:
Current maturities of long-term debt, net	0		0
Short-term borrowings	105,100		55,100
Payables to affiliates	0		0
Accounts payable	0		0
Accrued expenses and other liabilities	90		313
Total current liabilities	105,190		55,413
Deferred income taxes	1,599		1,520
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	888,812		836,839
Cal Water | Reportable Legal Entities
Utility plant:
Utility plant	3,478,007		3,332,331
Less accumulated depreciation and amortization	(1,127,493)		(1,079,627)
Net utility plant	2,350,514		2,252,704
Current assets:
Cash and cash equivalents	87,158		29,098
Receivables and unbilled revenue, net	116,442		114,999
Receivables from affiliates	831		3,621
Other current assets	26,448		20,615
Total current assets	230,879		168,333
Other assets:
Regulatory assets	436,197		428,639
Investments in affiliates	0		0
Long-term affiliate notes receivable	0		0
Other assets	79,519		81,591
Total other assets	515,716		510,230
TOTAL ASSETS	3,097,109		2,931,267
Capitalization:
Common stockholders’ equity	702,210		700,784
Affiliate long-term debt	0		0
Long-term debt, net	784,845		786,310
Total capitalization	1,487,055		1,487,094
Current liabilities:
Current maturities of long-term debt, net	21,753		21,732
Short-term borrowings	270,000		120,000
Payables to affiliates	409		6,115
Accounts payable	122,926		104,419
Accrued expenses and other liabilities	48,029		50,569
Total current liabilities	463,117		302,835
Deferred income taxes	215,464		217,847
Pension and postretirement benefits other than pensions	261,119		258,907
Regulatory liabilities and other	264,351		264,434
Advances for construction	194,542		190,568
Contributions in aid of construction	211,461		209,582
TOTAL CAPITALIZATION AND LIABILITIES	3,097,109		2,931,267
All Other Subsidiaries | Reportable Legal Entities
Utility plant:
Utility plant	280,115		224,033
Less accumulated depreciation and amortization	(87,999)		(65,561)
Net utility plant	192,116		158,472
Current assets:
Cash and cash equivalents	8,001		10,459
Receivables and unbilled revenue, net	6,587		4,350
Receivables from affiliates	143		209
Other current assets	2,571		2,005
Total current assets	17,302		17,023
Other assets:
Regulatory assets	4,789		4,683
Investments in affiliates	0		0
Long-term affiliate notes receivable	0		0
Other assets	34,521		5,125
Total other assets	39,310		9,808
TOTAL ASSETS	248,728		185,303
Capitalization:
Common stockholders’ equity	114,972		81,604
Affiliate long-term debt	33,160		30,060
Long-term debt, net	412		444
Total capitalization	148,544		112,108
Current liabilities:
Current maturities of long-term debt, net	119		136
Short-term borrowings	0		0
Payables to affiliates	23,956		23,518
Accounts payable	5,290		4,044
Accrued expenses and other liabilities	4,245		2,408
Total current liabilities	33,610		30,106
Deferred income taxes	6,901		3,243
Pension and postretirement benefits other than pensions	0		0
Regulatory liabilities and other	5,826		7,397
Advances for construction	514		494
Contributions in aid of construction	53,333		31,955
TOTAL CAPITALIZATION AND LIABILITIES	$ 248,728		$ 185,303