- Condensed Consolidating Statement of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating activities:
Net income (loss)	$ 11,336	$ 42,424	$ 16,996	$ (7,640)	$ 15,368	$ 36,173	$ 14,805	$ (762)	$ 63,116	$ 65,584	$ 72,940
Operating activities:
Equity earnings of subsidiaries									0	0	0
Dividends received from Affiliates									0	0	0
Depreciation and amortization									91,288	85,707	78,592
Change in value of life insurance contracts									(5,104)	2,334	(3,058)
Stock-based compensation									6,731	3,141	3,118
Gain on sale of non-utility properties									(28)	(50)	(663)
Changes in normalized deferred income taxes									15,346	20,909	21,087
Allowance for equity funds used during construction									(6,685)	(3,954)	(3,750)
Changes in operating assets and liabilities									2,424	16,483	(36,389)
Other changes in noncurrent assets and liabilities									1,706	(11,135)	15,965
Net cash provided by operating activities									168,794	179,019	147,842
Investing activities:
Utility plant expenditures									(273,770)	(271,707)	(259,194)
TCP settlement proceeds											56,004
Proceeds from sale of non-utility assets									28	59	666
Investment in affiliates									0
Change in affiliate advances									0	0	0
Issuance of affiliate short-term borrowings									0	0	0
Collection of affiliate short-term debt										0
Collection of affiliate long-term debt									0	0	0
Life insurance benefits									0	3,491	1,558
Purchase of life insurance									(2,216)	(4,925)	(5,605)
Net cash used in investing activities									(275,958)	(273,082)	(206,571)
Financing Activities:
Short-term borrowings									260,000	151,000	265,000
Repayment of short-term borrowings									(150,000)	(361,000)	(87,000)
Investment from affiliates									0
Change in affiliate advances									0	0	0
Proceeds from affiliate short-term borrowings										0	0
Repayment of affiliates short-term debt										0
Repayment of affiliates long-term debt									0	0	0
Issuance of long-term debt, net of debt issuance costs									398,204	299,383	0
Retirement of long-term debt									(405,568)	(16,532)	(26,829)
Advances and contributions in aid of construction									27,774	18,612	21,369
Refunds of advances for construction									(7,566)	(7,297)	(8,378)
Issuance of common stock									20,423	0	0
Repurchase of common stock									(2,497)	(1,645)	(1,505)
Dividends paid to non-affiliates									(38,023)	(36,043)	(34,563)
Dividends paid to affiliates									0	0	0
Net cash provided by financing activities									102,747	46,478	128,094
Change in cash, cash equivalents, and restricted cash									(4,417)	(47,585)	69,365
Cash, cash equivalents, and restricted cash at beginning of year				47,715				95,300	47,715	95,300	25,935
Cash, cash equivalents, and restricted cash at end of year	43,298				47,715				43,298	47,715	95,300
Consolidating Adjustments
Operating activities:
Net income (loss)									(62,685)	(64,768)	(72,433)
Operating activities:
Equity earnings of subsidiaries									62,745	64,748	72,487
Dividends received from Affiliates									(38,023)	(36,043)	(34,563)
Depreciation and amortization									(82)	(87)	(91)
Change in value of life insurance contracts									0	0	0
Stock-based compensation									0	0	0
Gain on sale of non-utility properties									0	0	0
Changes in normalized deferred income taxes									0	0	0
Allowance for equity funds used during construction									0	0	0
Changes in operating assets and liabilities									0	0	0
Other changes in noncurrent assets and liabilities									22	107	37
Net cash provided by operating activities									(38,023)	(36,043)	(34,563)
Investing activities:
Utility plant expenditures									0	0	0
TCP settlement proceeds											0
Proceeds from sale of non-utility assets									0	0	0
Investment in affiliates									19,294
Change in affiliate advances									4,100	617	363
Issuance of affiliate short-term borrowings									4,300	23,700	2,610
Collection of affiliate short-term debt										(20,000)
Collection of affiliate long-term debt									(1,963)	(1,635)	(1,356)
Life insurance benefits										0	0
Purchase of life insurance									0	0	0
Net cash used in investing activities									25,731	2,682	1,617
Financing Activities:
Short-term borrowings									0	0	0
Repayment of short-term borrowings									0	0	0
Investment from affiliates									(19,294)
Change in affiliate advances									(4,100)	(617)	(363)
Proceeds from affiliate short-term borrowings									(4,300)	(23,700)	(2,610)
Repayment of affiliates short-term debt										20,000
Repayment of affiliates long-term debt									1,963	1,635	1,356
Issuance of long-term debt, net of debt issuance costs									0	0
Retirement of long-term debt									0	0	0
Advances and contributions in aid of construction									0	0	0
Refunds of advances for construction									0	0	0
Issuance of common stock									0
Repurchase of common stock									0	0	0
Dividends paid to non-affiliates									0	0	0
Dividends paid to affiliates									38,023	36,043	34,563
Net cash provided by financing activities									12,292	33,361	32,946
Change in cash, cash equivalents, and restricted cash									0	0	0
Cash, cash equivalents, and restricted cash at beginning of year				0				0	0	0	0
Cash, cash equivalents, and restricted cash at end of year	0				0				0	0	0
Parent Company
Operating activities:
Net income (loss)											72,940
Operating activities:
Equity earnings of subsidiaries											(72,487)
Dividends received from Affiliates											34,563
Depreciation and amortization											94
Change in value of life insurance contracts											0
Stock-based compensation											3,118
Gain on sale of non-utility properties											0
Changes in normalized deferred income taxes											0
Allowance for equity funds used during construction											0
Changes in operating assets and liabilities											184
Other changes in noncurrent assets and liabilities											254
Net cash provided by operating activities											38,666
Investing activities:
Utility plant expenditures											(4)
TCP settlement proceeds											0
Proceeds from sale of non-utility assets											0
Change in affiliate advances											172
Issuance of affiliate short-term borrowings											(2,610)
Collection of affiliate long-term debt											1,356
Life insurance benefits											0
Purchase of life insurance											0
Net cash used in investing activities											(1,086)
Financing Activities:
Short-term borrowings											0
Repayment of short-term borrowings											(2,000)
Change in affiliate advances											0
Proceeds from affiliate short-term borrowings											0
Repayment of affiliates long-term debt											0
Retirement of long-term debt											0
Advances and contributions in aid of construction											0
Refunds of advances for construction											0
Repurchase of common stock											(1,505)
Dividends paid to non-affiliates											(34,563)
Dividends paid to affiliates											0
Net cash provided by financing activities											(38,068)
Change in cash, cash equivalents, and restricted cash											(488)
Cash, cash equivalents, and restricted cash at beginning of year								4,728		4,728	5,216
Cash, cash equivalents, and restricted cash at end of year											4,728
Parent Company | Reportable Legal Entities
Operating activities:
Net income (loss)									63,116	65,584	72,940
Operating activities:
Equity earnings of subsidiaries									(62,745)	(64,748)	(72,487)
Dividends received from Affiliates									38,023	36,043
Depreciation and amortization									94	94
Change in value of life insurance contracts									0	0
Stock-based compensation									0	3,141
Gain on sale of non-utility properties									0	0	0
Changes in normalized deferred income taxes									0	0
Allowance for equity funds used during construction									0	0	0
Changes in operating assets and liabilities									321	(290)
Other changes in noncurrent assets and liabilities									6,632	(348)
Net cash provided by operating activities									45,441	39,476
Investing activities:
Utility plant expenditures									0	0
Proceeds from sale of non-utility assets									0	0
Investment in affiliates									(19,294)
Change in affiliate advances									(4,379)	(689)
Issuance of affiliate short-term borrowings									(4,300)	(23,700)
Collection of affiliate short-term debt										20,000
Collection of affiliate long-term debt									1,963	1,635
Life insurance benefits										0
Purchase of life insurance									0	0
Net cash used in investing activities									(26,010)	(2,754)
Financing Activities:
Short-term borrowings									0	20,000
Repayment of short-term borrowings									0	(20,000)
Investment from affiliates									0
Change in affiliate advances									(17)	17
Proceeds from affiliate short-term borrowings									0	20,000
Repayment of affiliates short-term debt										(20,000)
Repayment of affiliates long-term debt									0	0
Issuance of long-term debt, net of debt issuance costs									0	0
Retirement of long-term debt									0	0
Advances and contributions in aid of construction									0	0
Refunds of advances for construction									0	0
Issuance of common stock									20,423
Repurchase of common stock									(2,497)	(1,645)
Dividends paid to non-affiliates									(38,023)	(36,043)
Dividends paid to affiliates									0	0
Net cash provided by financing activities									(20,114)	(37,671)
Change in cash, cash equivalents, and restricted cash									(683)	(949)
Cash, cash equivalents, and restricted cash at beginning of year				3,779				4,728	3,779	4,728
Cash, cash equivalents, and restricted cash at end of year	3,096				3,779				3,096	3,779	4,728
Cal Water
Operating activities:
Net income (loss)											70,071
Operating activities:
Equity earnings of subsidiaries											0
Dividends received from Affiliates											0
Depreciation and amortization											74,041
Change in value of life insurance contracts											(3,058)
Stock-based compensation											0
Gain on sale of non-utility properties											(663)
Changes in normalized deferred income taxes											21,087
Allowance for equity funds used during construction											(3,750)
Changes in operating assets and liabilities											(36,611)
Other changes in noncurrent assets and liabilities											13,101
Net cash provided by operating activities											134,218
Investing activities:
Utility plant expenditures											(252,055)
TCP settlement proceeds											56,004
Proceeds from sale of non-utility assets											666
Change in affiliate advances											(485)
Issuance of affiliate short-term borrowings											0
Collection of affiliate long-term debt											0
Life insurance benefits											1,558
Purchase of life insurance											(5,605)
Net cash used in investing activities											(199,917)
Financing Activities:
Short-term borrowings											265,000
Repayment of short-term borrowings											(85,000)
Change in affiliate advances											41
Proceeds from affiliate short-term borrowings											0
Repayment of affiliates long-term debt											0
Retirement of long-term debt											(26,223)
Advances and contributions in aid of construction											21,075
Refunds of advances for construction											(8,373)
Repurchase of common stock											0
Dividends paid to non-affiliates											0
Dividends paid to affiliates											(33,015)
Net cash provided by financing activities											133,505
Change in cash, cash equivalents, and restricted cash											67,806
Cash, cash equivalents, and restricted cash at beginning of year								81,401		81,401	13,595
Cash, cash equivalents, and restricted cash at end of year											81,401
Cal Water | Reportable Legal Entities
Operating activities:
Net income (loss)									58,447	61,905	70,071
Operating activities:
Equity earnings of subsidiaries									0	0	0
Dividends received from Affiliates									0	0
Depreciation and amortization									85,175	80,442
Change in value of life insurance contracts									(5,104)	2,334
Stock-based compensation									0	0
Gain on sale of non-utility properties									(28)	(50)	(663)
Changes in normalized deferred income taxes									15,346	20,909
Allowance for equity funds used during construction									(6,685)	(3,954)	(3,750)
Changes in operating assets and liabilities									1,883	16,943
Other changes in noncurrent assets and liabilities									(308)	(12,284)
Net cash provided by operating activities									148,726	166,245
Investing activities:
Utility plant expenditures									(262,500)	(261,456)
Proceeds from sale of non-utility assets									28	59
Investment in affiliates									0
Change in affiliate advances									453	19
Issuance of affiliate short-term borrowings									0	0
Collection of affiliate short-term debt										0
Collection of affiliate long-term debt									0	0
Life insurance benefits										3,491
Purchase of life insurance									(2,216)	(4,925)
Net cash used in investing activities									(264,235)	(262,812)
Financing Activities:
Short-term borrowings									260,000	131,000
Repayment of short-term borrowings									(150,000)	(341,000)
Investment from affiliates									19,294
Change in affiliate advances									5,627	(93)
Proceeds from affiliate short-term borrowings									0	0
Repayment of affiliates short-term debt										0
Repayment of affiliates long-term debt									0	0
Issuance of long-term debt, net of debt issuance costs									398,204	299,383
Retirement of long-term debt									(405,317)	(16,200)
Advances and contributions in aid of construction									27,005	18,218
Refunds of advances for construction									(7,565)	(7,279)
Issuance of common stock									0
Repurchase of common stock									0	0
Dividends paid to non-affiliates									0	0
Dividends paid to affiliates									(36,297)	(34,624)
Net cash provided by financing activities									110,951	49,405
Change in cash, cash equivalents, and restricted cash									(4,558)	(47,162)
Cash, cash equivalents, and restricted cash at beginning of year				34,239				81,401	34,239	81,401
Cash, cash equivalents, and restricted cash at end of year	29,681				34,239				29,681	34,239	81,401
All Other Subsidiaries
Operating activities:
Net income (loss)											2,362
Operating activities:
Equity earnings of subsidiaries											0
Dividends received from Affiliates											0
Depreciation and amortization											4,548
Change in value of life insurance contracts											0
Stock-based compensation											0
Gain on sale of non-utility properties											0
Changes in normalized deferred income taxes											0
Allowance for equity funds used during construction											0
Changes in operating assets and liabilities											38
Other changes in noncurrent assets and liabilities											2,573
Net cash provided by operating activities											9,521
Investing activities:
Utility plant expenditures											(7,135)
TCP settlement proceeds											0
Proceeds from sale of non-utility assets											0
Change in affiliate advances											(50)
Issuance of affiliate short-term borrowings											0
Collection of affiliate long-term debt											0
Life insurance benefits											0
Purchase of life insurance											0
Net cash used in investing activities											(7,185)
Financing Activities:
Short-term borrowings											0
Repayment of short-term borrowings											0
Change in affiliate advances											322
Proceeds from affiliate short-term borrowings											2,610
Repayment of affiliates long-term debt											(1,356)
Retirement of long-term debt											(606)
Advances and contributions in aid of construction											294
Refunds of advances for construction											(5)
Repurchase of common stock											0
Dividends paid to non-affiliates											0
Dividends paid to affiliates											(1,548)
Net cash provided by financing activities											(289)
Change in cash, cash equivalents, and restricted cash											2,047
Cash, cash equivalents, and restricted cash at beginning of year								9,171		9,171	7,124
Cash, cash equivalents, and restricted cash at end of year											9,171
All Other Subsidiaries | Reportable Legal Entities
Operating activities:
Net income (loss)									4,238	2,863	2,362
Operating activities:
Equity earnings of subsidiaries									0	0	0
Dividends received from Affiliates									0	0
Depreciation and amortization									6,101	5,258
Change in value of life insurance contracts									0	0
Stock-based compensation									6,731	0
Gain on sale of non-utility properties									0	0	0
Changes in normalized deferred income taxes									0	0
Allowance for equity funds used during construction									0	0	0
Changes in operating assets and liabilities									220	(170)
Other changes in noncurrent assets and liabilities									(4,640)	1,390
Net cash provided by operating activities									12,650	9,341
Investing activities:
Utility plant expenditures									(11,270)	(10,251)
Proceeds from sale of non-utility assets									0	0
Investment in affiliates									0
Change in affiliate advances									(174)	53
Issuance of affiliate short-term borrowings									0	0
Collection of affiliate short-term debt										0
Collection of affiliate long-term debt									0	0
Life insurance benefits										0
Purchase of life insurance									0	0
Net cash used in investing activities									(11,444)	(10,198)
Financing Activities:
Short-term borrowings									0	0
Repayment of short-term borrowings									0	0
Investment from affiliates									0
Change in affiliate advances									(1,510)	693
Proceeds from affiliate short-term borrowings									4,300	3,700
Repayment of affiliates short-term debt										0
Repayment of affiliates long-term debt									(1,963)	(1,635)
Issuance of long-term debt, net of debt issuance costs									0	0
Retirement of long-term debt									(251)	(332)
Advances and contributions in aid of construction									769	394
Refunds of advances for construction									(1)	(18)
Issuance of common stock									0
Repurchase of common stock									0	0
Dividends paid to non-affiliates									0	0
Dividends paid to affiliates									(1,726)	(1,419)
Net cash provided by financing activities									(382)	1,383
Change in cash, cash equivalents, and restricted cash									824	526
Cash, cash equivalents, and restricted cash at beginning of year				$ 9,697				$ 9,171	9,697	9,171
Cash, cash equivalents, and restricted cash at end of year	$ 10,521				$ 9,697				$ 10,521	$ 9,697	$ 9,171