Condensed Consolidating Financial Statements - Condensed Consolidating Statement of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Condensed Consolidating Financial Statements
Net Income (Loss) Attributable to Parent	$ (20,307)	$ (7,640)
Adjustments to reconcile net (loss) income to net cash provided by operating activities:
Equity loss of subsidiaries	0	0
Dividends received from affiliates	0	0
Depreciation and amortization	25,093	22,893
Change in value of life insurance contracts	4,717	(2,254)
Allowance for equity funds used during construction	(1,614)	(1,533)
Changes in operating assets and liabilities:
Changes in operating assets and liabilities	(570)	1,155
Other changes in noncurrent assets and liabilities	(3,252)	7,520
Net cash provided by operating activities	4,067	20,141
Investing activities:
Utility plant expenditures	(65,270)	(59,881)
Investment in affiliates	0
Changes in affiliate advances	0	0
Issuance of affiliate short-term borrowings	0	0
Reduction of affiliates long-term debt	0	0
Net cash used in investing activities	(65,270)	(59,881)
Financing Activities:
Short-term borrowings	170,000	60,000
Changes in affiliate advances		0
Proceeds from affiliate short-term borrowings		0
Repayment of short-term borrowings	(10,000)	0
Investment from affiliates	0
Changes in affiliate advances	0
Proceeds from affiliate short-term borrowings	0
Repayment of affiliates long-term borrowings	0	0
Repayment of long-term debt	(197)	(226)
Advances and contributions in aid of construction	6,432	6,044
Refunds of advances for construction	(2,157)	(1,790)
Repurchase of common stock	(1,373)	(2,074)
Issuance of common stock	6,511	454
Issuance of common stock		454
Dividends paid to non-affiliates	(10,315)	(9,493)
Dividends paid to affiliates	0	0
Net cash provided by financing activities	158,901	52,915
Change in cash, cash equivalents, and restricted cash	97,698	13,175
Cash, cash equivalents, and restricted cash at beginning of period	43,298	47,715
Cash, cash equivalents, and restricted cash at end of period	140,996	60,890
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect		13,175
Consolidating Adjustments
Condensed Consolidating Financial Statements
Net Income (Loss) Attributable to Parent	20,418	7,749
Adjustments to reconcile net (loss) income to net cash provided by operating activities:
Equity loss of subsidiaries	(20,404)	(7,734)
Dividends received from affiliates	(10,315)	(9,493)
Depreciation and amortization	(20)	(21)
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	6
Net cash provided by operating activities	(10,315)	(9,493)
Investing activities:
Utility plant expenditures	0	0
Investment in affiliates	(6,049)
Changes in affiliate advances	(8,052)	(1,401)
Issuance of affiliate short-term borrowings	3,500	4,300
Reduction of affiliates long-term debt	(592)	(481)
Net cash used in investing activities	905	2,418
Financing Activities:
Short-term borrowings	0	0
Changes in affiliate advances		1,401
Proceeds from affiliate short-term borrowings		(4,300)
Repayment of short-term borrowings	0
Investment from affiliates	(6,049)
Changes in affiliate advances	(8,052)
Proceeds from affiliate short-term borrowings	(3,500)
Repayment of affiliates long-term borrowings	(592)	(481)
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
Issuance of common stock		0
Dividends paid to non-affiliates	0	0
Dividends paid to affiliates	10,315	9,493
Net cash provided by financing activities	9,410	7,075
Change in cash, cash equivalents, and restricted cash	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
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect		0
Parent Company | Reportable Legal Entities
Condensed Consolidating Financial Statements
Net Income (Loss) Attributable to Parent	(20,307)	(7,640)
Adjustments to reconcile net (loss) income to net cash provided by operating activities:
Equity loss of subsidiaries	20,404	7,734
Dividends received from affiliates	10,315	9,493
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	(522)	(195)
Other changes in noncurrent assets and liabilities	704	2,476
Net cash provided by operating activities	10,617	11,891
Investing activities:
Utility plant expenditures	0	0
Investment in affiliates	6,049
Changes in affiliate advances	5,980	184
Issuance of affiliate short-term borrowings	(3,500)	(4,300)
Reduction of affiliates long-term debt	592	481
Net cash used in investing activities	(2,977)	(3,635)
Financing Activities:
Short-term borrowings	50,000	0
Changes in affiliate advances		(17)
Proceeds from affiliate short-term borrowings		0
Repayment of short-term borrowings	0
Investment from affiliates	0
Changes in affiliate advances	(797)
Proceeds from affiliate short-term borrowings	0
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	(1,373)	(2,074)
Issuance of common stock	6,511
Issuance of common stock		454
Dividends paid to non-affiliates	(10,315)	(9,493)
Dividends paid to affiliates	0	0
Net cash provided by financing activities	45,620	(11,130)
Change in cash, cash equivalents, and restricted cash	53,260
Cash, cash equivalents, and restricted cash at beginning of period	3,096	3,779
Cash, cash equivalents, and restricted cash at end of period	56,356	905
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect		(2,874)
Cal Water | Reportable Legal Entities
Condensed Consolidating Financial Statements
Net Income (Loss) Attributable to Parent	(20,467)	(7,941)
Adjustments to reconcile net (loss) income to net cash provided by operating activities:
Equity loss of subsidiaries	0	0
Dividends received from affiliates	0	0
Depreciation and amortization	23,525	21,394
Change in value of life insurance contracts	4,717	(2,254)
Allowance for equity funds used during construction	(1,614)	(1,533)
Changes in operating assets and liabilities:
Changes in operating assets and liabilities	(230)	(201)
Other changes in noncurrent assets and liabilities	(4,021)	4,951
Net cash provided by operating activities	1,910	14,416
Investing activities:
Utility plant expenditures	(62,671)	(57,410)
Investment in affiliates	0
Changes in affiliate advances	1,917	1,330
Issuance of affiliate short-term borrowings	0	0
Reduction of affiliates long-term debt	0	0
Net cash used in investing activities	(60,754)	(56,080)
Financing Activities:
Short-term borrowings	120,000	60,000
Changes in affiliate advances		772
Proceeds from affiliate short-term borrowings		0
Repayment of short-term borrowings	(10,000)
Investment from affiliates	6,049
Changes in affiliate advances	6,090
Proceeds from affiliate short-term borrowings	0
Repayment of affiliates long-term borrowings	0	0
Repayment of long-term debt	(166)	(171)
Advances and contributions in aid of construction	6,400	5,979
Refunds of advances for construction	(2,156)	(1,789)
Repurchase of common stock	0	0
Issuance of common stock	0
Issuance of common stock		0
Dividends paid to non-affiliates	0	0
Dividends paid to affiliates	(9,691)	(9,185)
Net cash provided by financing activities	104,346	55,606
Change in cash, cash equivalents, and restricted cash	45,502
Cash, cash equivalents, and restricted cash at beginning of period	29,679	34,238
Cash, cash equivalents, and restricted cash at end of period	75,181	48,180
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect		13,942
All Other Subsidiaries | Reportable Legal Entities
Condensed Consolidating Financial Statements
Net Income (Loss) Attributable to Parent	49	192
Adjustments to reconcile net (loss) income to net cash provided by operating activities:
Equity loss of subsidiaries	0	0
Dividends received from affiliates	0	0
Depreciation and amortization	1,565	1,497
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	182	1,551
Other changes in noncurrent assets and liabilities	59	87
Net cash provided by operating activities	1,855	3,327
Investing activities:
Utility plant expenditures	(2,599)	(2,471)
Investment in affiliates	0
Changes in affiliate advances	155	(113)
Issuance of affiliate short-term borrowings	0	0
Reduction of affiliates long-term debt	0	0
Net cash used in investing activities	(2,444)	(2,584)
Financing Activities:
Short-term borrowings	0	0
Changes in affiliate advances		(2,156)
Proceeds from affiliate short-term borrowings		4,300
Repayment of short-term borrowings	0
Investment from affiliates	0
Changes in affiliate advances	2,759
Proceeds from affiliate short-term borrowings	3,500
Repayment of affiliates long-term borrowings	592	481
Repayment of long-term debt	(31)	(55)
Advances and contributions in aid of construction	32	65
Refunds of advances for construction	(1)	(1)
Repurchase of common stock	0	0
Issuance of common stock	0
Issuance of common stock		0
Dividends paid to non-affiliates	0	0
Dividends paid to affiliates	(624)	(308)
Net cash provided by financing activities	(475)	1,364
Change in cash, cash equivalents, and restricted cash	(1,064)
Cash, cash equivalents, and restricted cash at beginning of period	10,523	9,698
Cash, cash equivalents, and restricted cash at end of period	$ 9,459	11,805
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect		$ 2,107