Condensed Consolidating Financial Statements - Condensed Consolidating Statement of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Condensed Consolidating Financial Statements
Net income	$ 96,360	$ 42,424	$ 81,334	$ 51,780
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			75,550	68,522
Change in value of life insurance contracts			(621)	(3,433)
Allowance for equity funds used during construction	(973)	(1,868)	(4,292)	(5,087)
Changes in operating assets and liabilities:
Changes in operating assets and liabilities			(18,407)	(5,041)
Other changes in noncurrent assets and liabilities			(36,900)	21,602
Net cash provided by operating activities			96,664	128,343
Investing activities:
Utility plant expenditures			(221,261)	(194,942)
Business acquisition, net of cash acquired			(39,544)	0
Investment in affiliates			0
Changes in affiliate advances			0	0
Issuance of affiliate short-term borrowings			0	0
Issuance of affiliate long-term borrowings			0
Reduction of affiliates long-term debt			0	0
Purchase of life insurance contracts			(2,335)	(2,216)
Net cash used in investing activities			(263,140)	(197,158)
Financing Activities:
Short-term borrowings			270,000	210,000
Repayment of short-term borrowings			(70,000)	(120,000)
Investment from affiliates			0
Changes in affiliate advances			0	0
Proceeds from affiliate short-term borrowings			0	0
Proceeds from affiliate long-term borrowings			0
Repayment of affiliates long-term borrowings			0	0
Issuance of long-term debt, net of expenses			0	398,431
Repayment of long-term debt			(1,535)	(401,630)
Advances and contributions in aid of construction			19,862	21,266
Refunds of advances for construction			(7,017)	(5,560)
Repurchase of common stock			(1,578)	(2,355)
Issuance of common stock			58,573	1,278
Dividends paid to non-affiliates			(31,177)	(28,507)
Dividends paid to affiliates			0	0
Net cash provided by financing activities			237,128	72,923
Change in cash, cash equivalents, and restricted cash			70,652	4,108
Cash, cash equivalents, and restricted cash at beginning of period			43,298	47,715
Cash, cash equivalents, and restricted cash at end of period	113,950	51,823	113,950	51,823
Consolidating Adjustments
Condensed Consolidating Financial Statements
Net income	(96,253)	(42,319)	(80,994)	(51,479)
Adjustments to reconcile net income to net cash provided by operating activities:
Equity earnings of subsidiaries	96,266	42,334	81,036	51,523
Dividends received from affiliates			(31,177)	(28,507)
Depreciation and amortization			(59)	(62)
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			17	18
Net cash provided by operating activities			(31,177)	(28,507)
Investing activities:
Utility plant expenditures			0	0
Business acquisition, net of cash acquired			0
Investment in affiliates			90,871
Changes in affiliate advances			(4,772)	(15)
Issuance of affiliate short-term borrowings			3,500	4,300
Issuance of affiliate long-term borrowings			4,076
Reduction of affiliates long-term debt			(1,580)	(1,462)
Purchase of life insurance contracts			0	0
Net cash used in investing activities			92,095	2,823
Financing Activities:
Short-term borrowings			0	0
Repayment of short-term borrowings			0	0
Investment from affiliates			(90,871)
Changes in affiliate advances			4,772	15
Proceeds from affiliate short-term borrowings			(3,500)	(4,300)
Proceeds from affiliate long-term borrowings			(4,076)
Repayment of affiliates long-term borrowings			1,580	1,462
Issuance of long-term debt, net of expenses				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	0
Dividends paid to non-affiliates			0	0
Dividends paid to affiliates			31,177	28,507
Net cash provided by financing activities			(60,918)	25,684
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	0	0
Parent Company | Reportable Legal Entities
Condensed Consolidating Financial Statements
Net income	96,360	42,424	81,334	51,780
Adjustments to reconcile net income to net cash provided by operating activities:
Equity earnings of subsidiaries	(96,266)	(42,334)	(81,036)	(51,523)
Dividends received from affiliates			31,177	28,507
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			(463)	194
Other changes in noncurrent assets and liabilities			3,262	5,239
Net cash provided by operating activities			34,344	34,267
Investing activities:
Utility plant expenditures			0	0
Business acquisition, net of cash acquired			(1,950)
Investment in affiliates			(90,871)
Changes in affiliate advances			2,238	(3,199)
Issuance of affiliate short-term borrowings			(3,500)	(4,300)
Issuance of affiliate long-term borrowings			(4,076)
Reduction of affiliates long-term debt			1,580	1,462
Purchase of life insurance contracts			0	0
Net cash used in investing activities			(96,579)	(6,037)
Financing Activities:
Short-term borrowings			50,000	0
Repayment of short-term borrowings			0	0
Investment from affiliates			0
Changes in affiliate advances			0	(17)
Proceeds from affiliate short-term borrowings			0	0
Proceeds from affiliate long-term borrowings			0
Repayment of affiliates long-term borrowings			0	0
Issuance of long-term debt, net of expenses				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			(1,578)	(2,355)
Issuance of common stock			58,573	1,278
Dividends paid to non-affiliates			(31,177)	(28,507)
Dividends paid to affiliates			0	0
Net cash provided by financing activities			75,818	(29,601)
Change in cash, cash equivalents, and restricted cash			13,583	(1,371)
Cash, cash equivalents, and restricted cash at beginning of period			3,096	3,779
Cash, cash equivalents, and restricted cash at end of period	16,679	2,408	16,679	2,408
Cal Water | Reportable Legal Entities
Condensed Consolidating Financial Statements
Net income	93,090	39,742	76,855	47,116
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			70,604	63,975
Change in value of life insurance contracts			(621)	(3,433)
Allowance for equity funds used during construction	(973)	(1,868)	(4,292)	(5,087)
Changes in operating assets and liabilities:
Changes in operating assets and liabilities			(17,633)	(6,744)
Other changes in noncurrent assets and liabilities			(42,184)	14,560
Net cash provided by operating activities			82,729	110,387
Investing activities:
Utility plant expenditures			(212,288)	(185,883)
Business acquisition, net of cash acquired			0
Investment in affiliates			0
Changes in affiliate advances			2,679	3,534
Issuance of affiliate short-term borrowings			0	0
Issuance of affiliate long-term borrowings			0
Reduction of affiliates long-term debt			0	0
Purchase of life insurance contracts			(2,335)	(2,216)
Net cash used in investing activities			(211,944)	(184,565)
Financing Activities:
Short-term borrowings			220,000	210,000
Repayment of short-term borrowings			(70,000)	(120,000)
Investment from affiliates			57,266
Changes in affiliate advances			(3,175)	4,419
Proceeds from affiliate short-term borrowings			0	0
Proceeds from affiliate long-term borrowings			0
Repayment of affiliates long-term borrowings			0	0
Issuance of long-term debt, net of expenses				398,431
Repayment of long-term debt			(1,415)	(401,417)
Advances and contributions in aid of construction			19,735	21,176
Refunds of advances for construction			(7,015)	(5,560)
Repurchase of common stock			0	0
Issuance of common stock			0	0
Dividends paid to non-affiliates			0	0
Dividends paid to affiliates			(29,461)	(27,419)
Net cash provided by financing activities			185,935	79,630
Change in cash, cash equivalents, and restricted cash			56,720	5,452
Cash, cash equivalents, and restricted cash at beginning of period			29,679	34,238
Cash, cash equivalents, and restricted cash at end of period	86,399	39,690	86,399	39,690
All Other Subsidiaries | Reportable Legal Entities
Condensed Consolidating Financial Statements
Net income	3,163	2,577	4,139	4,363
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			4,935	4,539
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			(311)	1,509
Other changes in noncurrent assets and liabilities			2,005	1,785
Net cash provided by operating activities			10,768	12,196
Investing activities:
Utility plant expenditures			(8,973)	(9,059)
Business acquisition, net of cash acquired			(37,594)
Investment in affiliates			0
Changes in affiliate advances			(145)	(320)
Issuance of affiliate short-term borrowings			0	0
Issuance of affiliate long-term borrowings			0
Reduction of affiliates long-term debt			0	0
Purchase of life insurance contracts			0	0
Net cash used in investing activities			(46,712)	(9,379)
Financing Activities:
Short-term borrowings			0	0
Repayment of short-term borrowings			0	0
Investment from affiliates			33,605
Changes in affiliate advances			(1,597)	(4,417)
Proceeds from affiliate short-term borrowings			3,500	4,300
Proceeds from affiliate long-term borrowings			4,076
Repayment of affiliates long-term borrowings			(1,580)	(1,462)
Issuance of long-term debt, net of expenses				0
Repayment of long-term debt			(120)	(213)
Advances and contributions in aid of construction			127	90
Refunds of advances for construction			(2)	0
Repurchase of common stock			0	0
Issuance of common stock			0	0
Dividends paid to non-affiliates			0	0
Dividends paid to affiliates			(1,716)	(1,088)
Net cash provided by financing activities			36,293	(2,790)
Change in cash, cash equivalents, and restricted cash			349	27
Cash, cash equivalents, and restricted cash at beginning of period			10,523	9,698
Cash, cash equivalents, and restricted cash at end of period	$ 10,872	$ 9,725	$ 10,872	$ 9,725