Condensed Consolidating Financial Statements - Condensed Consolidating Statement of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Operating activities:
Net loss	$ (7,640)	$ (762)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Equity loss of subsidiaries	0	0
Dividends received from affiliates	0	0
Depreciation and amortization	22,893	21,207
Change in value of life insurance contracts	(2,254)	1,137
Allowance for equity funds used during construction	(1,533)	(911)
Changes in operating assets and liabilities:
Changes in operating assets and liabilities	1,155	3,081
Other changes in noncurrent assets and liabilities	7,520	4,500
Net cash provided by operating activities	20,141	28,252
Investing activities:
Utility plant expenditures	(59,881)	(70,650)
Changes in affiliate advances	0	0
Issuance of affiliate short-term borrowings	0
Reduction of affiliates long-term debt	0	0
Net cash used in investing activities	(59,881)	(70,650)
Financing Activities:
Short-term borrowings	60,000	45,022
Repayment of short-term borrowings	0	(45,022)
Proceeds from affiliate short-term borrowings	0
Changes in affiliate advances	0	0
Repayment of affiliates long-term borrowings	0	0
Repayment of long-term debt	(226)	(10,224)
Advances and contributions in aid of construction	6,044	4,763
Refunds of advances for construction	(1,790)	(1,918)
Repurchase of common stock	(2,074)	(1,239)
Issuance of common stock	454	0
Dividends paid to non-affiliates	(9,493)	(9,003)
Dividends paid to affiliates	0	0
Net cash provided by (used in) financing activities	52,915	(17,621)
Change in cash, cash equivalents, and restricted cash	13,175	(60,019)
Cash, cash equivalents, and restricted cash at beginning of period	47,715	95,352
Cash, cash equivalents, and restricted cash at end of period	60,890	35,333
Consolidating Adjustments
Operating activities:
Net loss	7,749	957
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Equity loss of subsidiaries	(7,734)	(942)
Dividends received from affiliates	(9,493)	(9,003)
Depreciation and amortization	(21)	(22)
Change in value of life insurance contracts	0	0
Allowance for equity funds used during construction	0	0
Changes in operating assets and liabilities:
Changes in operating assets and liabilities	0	0
Other changes in noncurrent assets and liabilities	6	7
Net cash provided by operating activities	(9,493)	(9,003)
Investing activities:
Utility plant expenditures	0	0
Changes in affiliate advances	(1,401)	(562)
Issuance of affiliate short-term borrowings	4,300
Reduction of affiliates long-term debt	(481)	(395)
Net cash used in investing activities	2,418	(957)
Financing Activities:
Short-term borrowings	0	0
Repayment of short-term borrowings		0
Proceeds from affiliate short-term borrowings	(4,300)
Changes in affiliate advances	1,401	562
Repayment of affiliates long-term borrowings	481	395
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	9,493	9,003
Net cash provided by (used in) financing activities	7,075	9,960
Change in cash, cash equivalents, and restricted cash	0	0
Cash, cash equivalents, and restricted cash at beginning of period	0	0
Cash, cash equivalents, and restricted cash at end of period	0	0
Parent Company | Reportable Legal Entities
Operating activities:
Net loss	(7,640)	(762)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Equity loss of subsidiaries	7,734	942
Dividends received from affiliates	9,493	9,003
Depreciation and amortization	23	23
Change in value of life insurance contracts	0	0
Allowance for equity funds used during construction	0	0
Changes in operating assets and liabilities:
Changes in operating assets and liabilities	(195)	(376)
Other changes in noncurrent assets and liabilities	2,476	806
Net cash provided by operating activities	11,891	9,636
Investing activities:
Utility plant expenditures	0	0
Changes in affiliate advances	184	(2,520)
Issuance of affiliate short-term borrowings	(4,300)
Reduction of affiliates long-term debt	481	395
Net cash used in investing activities	(3,635)	(2,125)
Financing Activities:
Short-term borrowings	0	0
Repayment of short-term borrowings		0
Proceeds from affiliate short-term borrowings	0
Changes in affiliate advances	(17)	245
Repayment of affiliates long-term borrowings	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	(2,074)	(1,239)
Issuance of common stock	454
Dividends paid to non-affiliates	(9,493)	(9,003)
Dividends paid to affiliates	0	0
Net cash provided by (used in) financing activities	(11,130)	(9,997)
Change in cash, cash equivalents, and restricted cash	(2,874)	(2,486)
Cash, cash equivalents, and restricted cash at beginning of period	3,779	4,728
Cash, cash equivalents, and restricted cash at end of period	905	2,242
Cal Water | Reportable Legal Entities
Operating activities:
Net loss	(7,941)	(937)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Equity loss of subsidiaries	0	0
Dividends received from affiliates	0	0
Depreciation and amortization	21,394	20,081
Change in value of life insurance contracts	(2,254)	1,137
Allowance for equity funds used during construction	(1,533)	(911)
Changes in operating assets and liabilities:
Changes in operating assets and liabilities	(201)	1,728
Other changes in noncurrent assets and liabilities	4,951	3,585
Net cash provided by operating activities	14,416	24,683
Investing activities:
Utility plant expenditures	(57,410)	(67,841)
Changes in affiliate advances	1,330	3,235
Issuance of affiliate short-term borrowings	0
Reduction of affiliates long-term debt	0	0
Net cash used in investing activities	(56,080)	(64,606)
Financing Activities:
Short-term borrowings	60,000	45,022
Repayment of short-term borrowings		(45,022)
Proceeds from affiliate short-term borrowings	0
Changes in affiliate advances	772	(423)
Repayment of affiliates long-term borrowings	0	0
Repayment of long-term debt	(171)	(10,158)
Advances and contributions in aid of construction	5,979	4,663
Refunds of advances for construction	(1,789)	(1,908)
Repurchase of common stock	0	0
Issuance of common stock	0
Dividends paid to non-affiliates	0	0
Dividends paid to affiliates	(9,185)	(8,665)
Net cash provided by (used in) financing activities	55,606	(16,491)
Change in cash, cash equivalents, and restricted cash	13,942	(56,414)
Cash, cash equivalents, and restricted cash at beginning of period	34,238	81,453
Cash, cash equivalents, and restricted cash at end of period	48,180	25,039
All Other Subsidiaries | Reportable Legal Entities
Operating activities:
Net loss	192	(20)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Equity loss of subsidiaries	0	0
Dividends received from affiliates	0	0
Depreciation and amortization	1,497	1,125
Change in value of life insurance contracts	0	0
Allowance for equity funds used during construction	0	0
Changes in operating assets and liabilities:
Changes in operating assets and liabilities	1,551	1,729
Other changes in noncurrent assets and liabilities	87	102
Net cash provided by operating activities	3,327	2,936
Investing activities:
Utility plant expenditures	(2,471)	(2,809)
Changes in affiliate advances	(113)	(153)
Issuance of affiliate short-term borrowings	0
Reduction of affiliates long-term debt	0	0
Net cash used in investing activities	(2,584)	(2,962)
Financing Activities:
Short-term borrowings	0	0
Repayment of short-term borrowings		0
Proceeds from affiliate short-term borrowings	4,300
Changes in affiliate advances	(2,156)	(384)
Repayment of affiliates long-term borrowings	(481)	(395)
Repayment of long-term debt	(55)	(66)
Advances and contributions in aid of construction	65	100
Refunds of advances for construction	(1)	(10)
Repurchase of common stock	0	0
Issuance of common stock	0
Dividends paid to non-affiliates	0	0
Dividends paid to affiliates	(308)	(338)
Net cash provided by (used in) financing activities	1,364	(1,093)
Change in cash, cash equivalents, and restricted cash	2,107	(1,119)
Cash, cash equivalents, and restricted cash at beginning of period	9,698	9,171
Cash, cash equivalents, and restricted cash at end of period	$ 11,805	$ 8,052