Condensed Consolidating Financial Statements - Condensed Consolidating Statement of (Loss) Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Condensed Consolidating Financial Statements
Operating revenue	$ 125,563	$ 126,111
Operations:
Water production costs	53,976	45,592
Administrative and general	29,680	29,097
Other operations	13,974	17,821
Maintenance	7,073	6,455
Depreciation and amortization	24,492	22,368
Income tax (benefit) expense	(3,937)	(2,991)
Property and other taxes	7,228	7,293
Total operating (income) expenses	132,486	125,635
Net operating income (loss)	(6,923)	476
Other income and expenses:
Non-regulated revenue	3,827	4,901
Non-regulated expenses	(8,454)	(2,219)
Other components of net periodic benefit cost	(1,430)	(1,259)
Allowance for equity funds used during construction	1,614	1,533
Income tax benefit (expense) on other income and expenses	913	(828)
Net other income	(3,530)	2,128
Interest expense:
Interest expense	10,798	11,075
Allowance for borrowed funds used during construction	(944)	(831)
Net interest expense	9,854	10,244
Equity loss of subsidiaries	0	0
Net (loss) income	(20,307)	(7,640)
Consolidating Adjustments
Condensed Consolidating Financial Statements
Operating revenue	0	0
Operations:
Water production costs	0	0
Administrative and general	0	0
Other operations	(146)	(146)
Maintenance	0	0
Depreciation and amortization	(20)	(21)
Income tax (benefit) expense	202	218
Property and other taxes	0	0
Total operating (income) expenses	36	51
Net operating income (loss)	(36)	(51)
Other income and expenses:
Non-regulated revenue	(700)	(759)
Non-regulated expenses	0	0
Other components of net periodic benefit cost	0	0
Allowance for equity funds used during construction	0	0
Income tax benefit (expense) on other income and expenses	196	212
Net other income	(504)	(547)
Interest expense:
Interest expense	(554)	(613)
Allowance for borrowed funds used during construction	0	0
Net interest expense	(554)	(613)
Equity loss of subsidiaries	20,404	7,734
Net (loss) income	20,418	7,749
Parent Company | Reportable Legal Entities
Condensed Consolidating Financial Statements
Operating revenue	0	0
Operations:
Water production costs	0	0
Administrative and general	0	0
Other operations	0	0
Maintenance	0	0
Depreciation and amortization	24	23
Income tax (benefit) expense	(118)	(135)
Property and other taxes	0	0
Total operating (income) expenses	(94)	(112)
Net operating income (loss)	94	112
Other income and expenses:
Non-regulated revenue	555	613
Non-regulated expenses	0	0
Other components of net periodic benefit cost	0	0
Allowance for equity funds used during construction	0	0
Income tax benefit (expense) on other income and expenses	(155)	(172)
Net other income	400	441
Interest expense:
Interest expense	397	459
Allowance for borrowed funds used during construction	0	0
Net interest expense	397	459
Equity loss of subsidiaries	(20,404)	(7,734)
Net (loss) income	(20,307)	(7,640)
Cal Water | Reportable Legal Entities
Condensed Consolidating Financial Statements
Operating revenue	115,392	116,074
Operations:
Water production costs	51,758	43,426
Administrative and general	26,892	26,203
Other operations	12,155	16,122
Maintenance	6,649	6,223
Depreciation and amortization	22,957	20,887
Income tax (benefit) expense	(4,022)	(3,105)
Property and other taxes	6,426	6,506
Total operating (income) expenses	122,815	116,262
Net operating income (loss)	(7,423)	(188)
Other income and expenses:
Non-regulated revenue	3,591	4,628
Non-regulated expenses	(8,255)	(2,038)
Other components of net periodic benefit cost	(1,401)	(1,229)
Allowance for equity funds used during construction	1,614	1,533
Income tax benefit (expense) on other income and expenses	918	(810)
Net other income	(3,533)	2,084
Interest expense:
Interest expense	10,400	10,613
Allowance for borrowed funds used during construction	(889)	(776)
Net interest expense	9,511	9,837
Equity loss of subsidiaries	0	0
Net (loss) income	(20,467)	(7,941)
All Other Subsidiaries | Reportable Legal Entities
Condensed Consolidating Financial Statements
Operating revenue	10,171	10,037
Operations:
Water production costs	2,218	2,166
Administrative and general	2,788	2,894
Other operations	1,965	1,845
Maintenance	424	232
Depreciation and amortization	1,531	1,479
Income tax (benefit) expense	1	31
Property and other taxes	802	787
Total operating (income) expenses	9,729	9,434
Net operating income (loss)	442	603
Other income and expenses:
Non-regulated revenue	381	419
Non-regulated expenses	(199)	(181)
Other components of net periodic benefit cost	(29)	(30)
Allowance for equity funds used during construction	0	0
Income tax benefit (expense) on other income and expenses	(46)	(58)
Net other income	107	150
Interest expense:
Interest expense	555	616
Allowance for borrowed funds used during construction	(55)	(55)
Net interest expense	500	561
Equity loss of subsidiaries	0	0
Net (loss) income	$ 49	$ 192