Condensed Consolidating Financial Statements - Condensed Consolidating Statement of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Operating activities:
Net income	$ 42,424	$ 16,996	$ (7,640)	$ 36,173	$ 14,805	$ (762)	$ 51,780	$ 50,216
Adjustments to reconcile net income to net cash provided by operating activities:
Equity earnings of subsidiaries	0			0			0	0
Dividends received from affiliates							0	0
Depreciation and amortization							68,522	64,131
Change in value of life insurance contracts							(3,433)	124
Allowance for equity funds used during construction	(1,868)			(1,023)			(5,087)	(2,644)
Changes in operating assets and liabilities:
Changes in operating assets and liabilities							(5,041)	7,032
Other changes in noncurrent assets and liabilities							21,602	644
Net cash provided by operating activities							128,343	119,503
Investing activities:
Utility plant expenditures							(194,942)	(212,856)
Changes in affiliate advances							0	0
Issuance of affiliate short-term borrowings							0	0
Reduction of affiliates long-term debt							0	0
Life insurance proceeds							0	3,491
Purchase of life insurance contracts							(2,216)	(4,925)
Net cash used in investing activities							(197,158)	(214,290)
Financing Activities:
Short-term borrowings							210,000	141,000
Repayment of short-term borrowings							(120,000)	(341,000)
Changes in affiliate advances							0	0
Proceeds from affiliate short-term borrowings							0	0
Repayment of affiliates long-term borrowings							0	0
Issuance of long term debt, net of expenses							398,431	299,383
Repayment of long-term debt							(401,630)	(12,499)
Advances and contributions in aid of construction							21,266	13,630
Refunds of advances for construction							(5,560)	(5,462)
Repurchase of common stock							(2,355)	(1,496)
Issuance of common stock							1,278	0
Dividends paid to non-affiliates							(28,507)	(27,029)
Dividends paid to affiliates							0	0
Net cash provided by financing activities							72,923	66,527
Change in cash, cash equivalents, and restricted cash							4,108	(28,260)
Cash, cash equivalents, and restricted cash at beginning of period			47,715			95,352	47,715	95,352
Cash, cash equivalents, and restricted cash at end of period	51,823			67,092			51,823	67,092
Consolidating Adjustments
Operating activities:
Net income	(42,319)			(36,073)			(51,479)	(49,816)
Adjustments to reconcile net income to net cash provided by operating activities:
Equity earnings of subsidiaries	42,334			36,088			51,523	49,863
Dividends received from affiliates							(28,507)	(27,029)
Depreciation and amortization							(62)	(65)
Change in value of life insurance contracts							0	0
Allowance for equity funds used during construction	0			0			0	0
Changes in operating assets and liabilities:
Changes in operating assets and liabilities							0	0
Other changes in noncurrent assets and liabilities							18	18
Net cash provided by operating activities							(28,507)	(27,029)
Investing activities:
Utility plant expenditures							0	0
Changes in affiliate advances							(15)	(1,954)
Issuance of affiliate short-term borrowings							4,300	23,700
Reduction of affiliates long-term debt							(1,462)	(1,224)
Life insurance proceeds								0
Purchase of life insurance contracts							0	0
Net cash used in investing activities							2,823	20,522
Financing Activities:
Short-term borrowings							0	0
Repayment of short-term borrowings							0	0
Changes in affiliate advances							15	1,954
Proceeds from affiliate short-term borrowings							(4,300)	(23,700)
Repayment of affiliates long-term borrowings							1,462	1,224
Issuance of long term debt, net of expenses							0	0
Repayment of long-term debt							0	0
Advances and contributions in aid of construction							0	0
Refunds of advances for construction							0	0
Repurchase of common stock							0	0
Issuance of common stock							0
Dividends paid to non-affiliates							0	0
Dividends paid to affiliates							28,507	27,029
Net cash provided by financing activities							25,684	6,507
Change in cash, cash equivalents, and restricted cash							0	0
Cash, cash equivalents, and restricted cash at beginning of period			0			0	0	0
Cash, cash equivalents, and restricted cash at end of period	0			0			0	0
Parent Company | Reportable Legal Entities
Operating activities:
Net income	42,424			36,173			51,780	50,216
Adjustments to reconcile net income to net cash provided by operating activities:
Equity earnings of subsidiaries	(42,334)			(36,088)			(51,523)	(49,863)
Dividends received from affiliates							28,507	27,029
Depreciation and amortization							70	70
Change in value of life insurance contracts							0	0
Allowance for equity funds used during construction	0			0			0	0
Changes in operating assets and liabilities:
Changes in operating assets and liabilities							194	(281)
Other changes in noncurrent assets and liabilities							5,239	2,518
Net cash provided by operating activities							34,267	29,689
Investing activities:
Utility plant expenditures							0	4
Changes in affiliate advances							(3,199)	(975)
Issuance of affiliate short-term borrowings							(4,300)	(23,700)
Reduction of affiliates long-term debt							1,462	1,224
Life insurance proceeds								0
Purchase of life insurance contracts							0	0
Net cash used in investing activities							(6,037)	(23,447)
Financing Activities:
Short-term borrowings							0	20,000
Repayment of short-term borrowings							0	0
Changes in affiliate advances							(17)	0
Proceeds from affiliate short-term borrowings							0	0
Repayment of affiliates long-term borrowings							0	0
Issuance of long term debt, net of expenses							0	0
Repayment of long-term debt							0	0
Advances and contributions in aid of construction							0	0
Refunds of advances for construction							0	0
Repurchase of common stock							(2,355)	(1,496)
Issuance of common stock							1,278
Dividends paid to non-affiliates							(28,507)	(27,029)
Dividends paid to affiliates							0	0
Net cash provided by financing activities							(29,601)	(8,525)
Change in cash, cash equivalents, and restricted cash							(1,371)	(2,283)
Cash, cash equivalents, and restricted cash at beginning of period			3,779			4,728	3,779	4,728
Cash, cash equivalents, and restricted cash at end of period	2,408			2,445			2,408	2,445
Cal Water | Reportable Legal Entities
Operating activities:
Net income	39,742			34,853			47,116	47,595
Adjustments to reconcile net income to net cash provided by operating activities:
Equity earnings of subsidiaries	0			0			0	0
Dividends received from affiliates							0	0
Depreciation and amortization							63,975	60,298
Change in value of life insurance contracts							(3,433)	124
Allowance for equity funds used during construction	(1,868)			(1,023)			(5,087)	(2,644)
Changes in operating assets and liabilities:
Changes in operating assets and liabilities							(6,744)	6,135
Other changes in noncurrent assets and liabilities							14,560	(3,881)
Net cash provided by operating activities							110,387	107,627
Investing activities:
Utility plant expenditures							(185,883)	(205,218)
Changes in affiliate advances							3,534	3,198
Issuance of affiliate short-term borrowings							0	0
Reduction of affiliates long-term debt							0	0
Life insurance proceeds								3,491
Purchase of life insurance contracts							(2,216)	(4,925)
Net cash used in investing activities							(184,565)	(203,454)
Financing Activities:
Short-term borrowings							210,000	121,000
Repayment of short-term borrowings							(120,000)	(341,000)
Changes in affiliate advances							4,419	1,129
Proceeds from affiliate short-term borrowings							0	20,000
Repayment of affiliates long-term borrowings							0	0
Issuance of long term debt, net of expenses							398,431	299,383
Repayment of long-term debt							(401,417)	(12,299)
Advances and contributions in aid of construction							21,176	13,288
Refunds of advances for construction							(5,560)	(5,452)
Repurchase of common stock							0	0
Issuance of common stock							0
Dividends paid to non-affiliates							0	0
Dividends paid to affiliates							(27,419)	(25,959)
Net cash provided by financing activities							79,630	70,090
Change in cash, cash equivalents, and restricted cash							5,452	(25,737)
Cash, cash equivalents, and restricted cash at beginning of period			34,238			81,453	34,238	81,453
Cash, cash equivalents, and restricted cash at end of period	39,690			55,716			39,690	55,716
All Other Subsidiaries | Reportable Legal Entities
Operating activities:
Net income	2,577			1,220			4,363	2,221
Adjustments to reconcile net income to net cash provided by operating activities:
Equity earnings of subsidiaries	0			0			0	0
Dividends received from affiliates							0	0
Depreciation and amortization							4,539	3,828
Change in value of life insurance contracts							0	0
Allowance for equity funds used during construction	0			0			0	0
Changes in operating assets and liabilities:
Changes in operating assets and liabilities							1,509	1,178
Other changes in noncurrent assets and liabilities							1,785	1,989
Net cash provided by operating activities							12,196	9,216
Investing activities:
Utility plant expenditures							(9,059)	(7,642)
Changes in affiliate advances							(320)	(269)
Issuance of affiliate short-term borrowings							0	0
Reduction of affiliates long-term debt							0	0
Life insurance proceeds								0
Purchase of life insurance contracts							0	0
Net cash used in investing activities							(9,379)	(7,911)
Financing Activities:
Short-term borrowings							0	0
Repayment of short-term borrowings							0	0
Changes in affiliate advances							(4,417)	(3,083)
Proceeds from affiliate short-term borrowings							4,300	3,700
Repayment of affiliates long-term borrowings							(1,462)	(1,224)
Issuance of long term debt, net of expenses							0	0
Repayment of long-term debt							(213)	(200)
Advances and contributions in aid of construction							90	342
Refunds of advances for construction							0	(10)
Repurchase of common stock							0	0
Issuance of common stock							0
Dividends paid to non-affiliates							0	0
Dividends paid to affiliates							(1,088)	(1,070)
Net cash provided by financing activities							(2,790)	(1,545)
Change in cash, cash equivalents, and restricted cash							27	(240)
Cash, cash equivalents, and restricted cash at beginning of period			$ 9,698			$ 9,171	9,698	9,171
Cash, cash equivalents, and restricted cash at end of period	$ 9,725			$ 8,931			$ 9,725	$ 8,931