Condensed Consolidating Financial Statements - Condensed Consolidating Balance Sheet (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Utility plant:
Utility plant	$ 3,346,165		$ 3,229,446
Less accumulated depreciation and amortization	(1,043,960)		(996,723)
Net utility plant	2,302,205		2,232,723
Current assets:
Cash and cash equivalents	54,560		47,176
Receivables and unbilled revenue	127,361		122,959
Receivables from affiliates	0		0
Other current assets	24,109		18,567
Total current assets	206,030		188,702
Other assets:
Regulatory assets	373,619		353,569
Investments in affiliates	0		0
Long-term affiliate notes receivable	0		0
Other assets	82,741		62,710
Total other assets	456,360		416,279
TOTAL ASSETS	2,964,595		2,837,704
Capitalization:
Common stockholders' equity	723,164	$ 714,129	730,157	$ 695,257	$ 688,853	$ 699,221	$ 699,221
Affiliate long-term debt	0		0
Long-term debt, net	807,693		710,027
Total capitalization	1,530,857		1,440,184
Current liabilities:
Current maturities of long-term debt, net	5,312		104,911
Short-term borrowings	165,100		65,100
Payables to affiliates	0		0
Accounts payable	97,376		95,580
Accrued expenses and other liabilities	63,601		55,575
Total current liabilities	331,389		321,166
Unamortized investment tax credits	1,649		1,649
Deferred income taxes	216,880		213,033
Pension and postretirement benefits other than pensions	201,476		193,538
Regulatory liabilities and other	264,027		256,522
Advances for construction	189,642		186,342
Contributions in aid of construction	228,675		225,270
TOTAL CAPITALIZATION AND LIABILITIES	2,964,595		2,837,704
Consolidating Adjustments
Utility plant:
Utility plant	(7,197)		(7,197)
Less accumulated depreciation and amortization	2,139		2,097
Net utility plant	(5,058)		(5,100)
Current assets:
Cash and cash equivalents	0		0
Receivables and unbilled revenue	0		0
Receivables from affiliates	(28,422)		(25,453)
Other current assets	0		0
Total current assets	(28,422)		(25,453)
Other assets:
Regulatory assets	0		0
Investments in affiliates	(723,345)		(733,156)
Long-term affiliate notes receivable	(26,965)		(27,829)
Other assets	(236)		(203)
Total other assets	(750,546)		(761,188)
TOTAL ASSETS	(784,026)		(791,741)
Capitalization:
Common stockholders' equity	(728,592)		(738,433)
Affiliate long-term debt	0		(27,828)
Long-term debt, net	(26,965)		0
Total capitalization	(755,557)		(766,261)
Current liabilities:
Current maturities of long-term debt, net	0		0
Short-term borrowings	0		0
Payables to affiliates	(28,422)		(25,453)
Accounts payable	0		0
Accrued expenses and other liabilities	0		0
Total current liabilities	(28,422)		(25,453)
Unamortized investment tax credits	0		0
Deferred income taxes	(32)		(43)
Pension and postretirement benefits other than pensions	0		0
Regulatory liabilities and other	(15)		16
Advances for construction	0		0
Contributions in aid of construction	0		0
TOTAL CAPITALIZATION AND LIABILITIES	(784,026)		(791,741)
Parent Company | Reportable Legal Entities
Utility plant:
Utility plant	1,318		1,318
Less accumulated depreciation and amortization	(1,060)		(1,013)
Net utility plant	258		305
Current assets:
Cash and cash equivalents	1,523		3,779
Receivables and unbilled revenue	0		126
Receivables from affiliates	27,087		21,318
Other current assets	379		80
Total current assets	28,989		25,303
Other assets:
Regulatory assets	0		0
Investments in affiliates	723,345		733,156
Long-term affiliate notes receivable	26,965		27,829
Other assets	490		133
Total other assets	750,800		761,118
TOTAL ASSETS	780,047		786,726
Capitalization:
Common stockholders' equity	723,164		730,157
Affiliate long-term debt	0		0
Long-term debt, net	0		0
Total capitalization	723,164		730,157
Current liabilities:
Current maturities of long-term debt, net	0		0
Short-term borrowings	55,100		55,100
Payables to affiliates	0		17
Accounts payable	0		0
Accrued expenses and other liabilities	343		107
Total current liabilities	55,443		55,224
Unamortized investment tax credits	0		0
Deferred income taxes	1,440		1,376
Pension and postretirement benefits other than pensions	0		0
Regulatory liabilities and other	0		(31)
Advances for construction	0		0
Contributions in aid of construction	0		0
TOTAL CAPITALIZATION AND LIABILITIES	780,047		786,726
Cal Water | Reportable Legal Entities
Utility plant:
Utility plant	3,132,488		3,021,437
Less accumulated depreciation and amortization	(981,960)		(938,072)
Net utility plant	2,150,528		2,083,365
Current assets:
Cash and cash equivalents	44,079		33,763
Receivables and unbilled revenue	121,618		118,632
Receivables from affiliates	1,219		4,074
Other current assets	21,840		16,907
Total current assets	188,756		173,376
Other assets:
Regulatory assets	369,320		349,414
Investments in affiliates	0		0
Long-term affiliate notes receivable	0		0
Other assets	77,721		58,959
Total other assets	447,041		408,373
TOTAL ASSETS	2,786,325		2,665,114
Capitalization:
Common stockholders' equity	648,366		659,340
Affiliate long-term debt	0		0
Long-term debt, net	807,163		709,444
Total capitalization	1,455,529		1,368,784
Current liabilities:
Current maturities of long-term debt, net	5,113		104,664
Short-term borrowings	110,000		10,000
Payables to affiliates	2,917		488
Accounts payable	93,307		92,310
Accrued expenses and other liabilities	59,872		53,655
Total current liabilities	271,209		261,117
Unamortized investment tax credits	1,649		1,649
Deferred income taxes	213,236		210,052
Pension and postretirement benefits other than pensions	201,476		193,538
Regulatory liabilities and other	257,124		250,720
Advances for construction	189,152		185,843
Contributions in aid of construction	196,950		193,411
TOTAL CAPITALIZATION AND LIABILITIES	2,786,325		2,665,114
All Other Subsidiaries | Reportable Legal Entities
Utility plant:
Utility plant	219,556		213,888
Less accumulated depreciation and amortization	(63,079)		(59,735)
Net utility plant	156,477		154,153
Current assets:
Cash and cash equivalents	8,958		9,634
Receivables and unbilled revenue	5,743		4,201
Receivables from affiliates	116		61
Other current assets	1,890		1,580
Total current assets	16,707		15,476
Other assets:
Regulatory assets	4,299		4,155
Investments in affiliates	0		0
Long-term affiliate notes receivable	0		0
Other assets	4,766		3,821
Total other assets	9,065		7,976
TOTAL ASSETS	182,249		177,605
Capitalization:
Common stockholders' equity	80,226		79,093
Affiliate long-term debt	0		27,828
Long-term debt, net	27,495		583
Total capitalization	107,721		107,504
Current liabilities:
Current maturities of long-term debt, net	199		247
Short-term borrowings	0		0
Payables to affiliates	25,505		24,948
Accounts payable	4,069		3,270
Accrued expenses and other liabilities	3,386		1,813
Total current liabilities	33,159		30,278
Unamortized investment tax credits	0		0
Deferred income taxes	2,236		1,648
Pension and postretirement benefits other than pensions	0		0
Regulatory liabilities and other	6,918		5,817
Advances for construction	490		499
Contributions in aid of construction	31,725		31,859
TOTAL CAPITALIZATION AND LIABILITIES	$ 182,249		$ 177,605