CONDENSED CONSOLIDATING FINANCIAL STATEMENTS (Details 4) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating activities:
Net income (loss)	$ 65,584	$ 72,940	$ 48,675
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Equity earnings of subsidiaries	0	0	0
Dividends received from affiliates	0	0	0
Depreciation and amortization	85,707	78,592	65,203
Amortization of debt premium and expenses	1,099	920	871
Change in value of life insurance contracts	2,334	(3,058)	(1,026)
Stock-based compensation	3,141	3,118	2,849
(Gain) loss on sale of non-utility property	(50)	(663)	146
Write-off of capital costs	410	1,293	3,221
Changes in normalized deferred income taxes	20,909	21,087	26,818
Allowance for equity funds used during construction	(3,954)	(3,750)	0
Changes in operating assets and liabilities	16,483	(36,389)	6,781
Other changes in noncurrent assets and liabilities	(11,135)	15,965	6,906
Net cash provided by operating activities	179,019	147,842	160,444
Investing activities:
Utility plant expenditures	(271,707)	(259,194)	(228,938)
TCP settlement proceeds	0	56,004	0
Proceeds from sale of non-utility properties	59	666	395
Change in affiliate advances	0	0	0
Collection of affiliate short-term borrowings	0		0
Life insurance benefits	3,491	1,558	495
Issuance of affiliate short-term borrowings	0	0	0
Collection of affiliate long-term debt	0	0	0
Purchase of life insurance contracts	(4,925)	(5,605)	(2,857)
Change in restricted cash		0	0
Net cash used in investing activities	(273,082)	(206,571)	(230,905)
Financing Activities:
Short-term borrowings	151,000	265,000	145,100
Repayment of short-term borrowings	(361,000)	(87,000)	(81,615)
Change in affiliate advances	0	0	0
Proceeds from affiliate short-term borrowings	0	0	0
Repayment of affiliate short-term borrowings	0		0
Repayment of affiliate long-term debt	0	0	0
Issuance of long-term debt, net	299,383	0	49,823
Repayment of long-term debt	(16,532)	(26,829)	(6,996)
Repurchase of common stock	(1,645)	(1,505)	(744)
Advances and contributions in aid of construction	18,612	21,369	21,448
Refunds of advances for construction	(7,297)	(8,378)	(6,885)
Dividends paid to non-affiliates	(36,043)	(34,563)	(33,081)
Dividends paid to affiliates	0	0	0
Net cash provided by financing activities	46,478	128,094	87,050
Change in cash, cash equivalents, and restricted cash	(47,585)	69,365	16,589
Cash, cash equivalents, and restricted cash at beginning of year	95,300	25,935	9,346
Cash, cash equivalents, and restricted cash at end of year	47,715	95,300	25,935
Reportable Legal Entities
Operating activities:
Net income (loss)	65,584	72,940
Consolidating Adjustments
Operating activities:
Net income (loss)	(64,768)	(72,433)	(48,101)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Equity earnings of subsidiaries	64,748	72,487	48,158
Dividends received from affiliates	(36,043)	(34,563)	(33,081)
Depreciation and amortization	(87)	(91)	(96)
Amortization of debt premium and expenses			0
Change in value of life insurance contracts	0	0	0
Stock-based compensation	0	0	0
(Gain) loss on sale of non-utility property	0	0	0
Write-off of capital costs			0
Changes in normalized deferred income taxes	0	0	0
Allowance for equity funds used during construction	0	0
Changes in operating assets and liabilities	0	0	0
Other changes in noncurrent assets and liabilities	107	37	39
Net cash provided by operating activities	(36,043)	(34,563)	(33,081)
Investing activities:
Utility plant expenditures	0	0	0
TCP settlement proceeds		0
Proceeds from sale of non-utility properties	0	0	0
Change in affiliate advances	617	363	(1,335)
Collection of affiliate short-term borrowings	(20,000)		(42,465)
Life insurance benefits	0	0	0
Issuance of affiliate short-term borrowings	23,700	2,610	22,965
Collection of affiliate long-term debt	(1,635)	(1,356)	(1,175)
Purchase of life insurance contracts	0	0	0
Net cash used in investing activities	2,682	1,617	(22,010)
Financing Activities:
Short-term borrowings	0	0	0
Repayment of short-term borrowings	0	0	0
Change in affiliate advances	(617)	(363)	1,335
Proceeds from affiliate short-term borrowings	(23,700)	(2,610)	(22,965)
Repayment of affiliate short-term borrowings	20,000		42,465
Repayment of affiliate long-term debt	1,635	1,356	1,175
Issuance of long-term debt, net	0		0
Repayment of long-term debt	0	0	0
Repurchase of common stock	0	0	0
Advances and contributions in aid of construction	0	0	0
Refunds of advances for construction	0	0	0
Dividends paid to non-affiliates	0	0	0
Dividends paid to affiliates	36,043	34,563	33,081
Net cash provided by financing activities	33,361	32,946	55,091
Change in cash, cash equivalents, and restricted cash	0	0	0
Cash, cash equivalents, and restricted cash at beginning of year	0	0	0
Cash, cash equivalents, and restricted cash at end of year	0	0	0
Parent Company
Operating activities:
Net income (loss)			48,675
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Equity earnings of subsidiaries			(48,158)
Dividends received from affiliates			33,081
Depreciation and amortization			220
Amortization of debt premium and expenses			0
Change in value of life insurance contracts			0
Stock-based compensation			2,849
(Gain) loss on sale of non-utility property			0
Write-off of capital costs			0
Changes in normalized deferred income taxes			0
Changes in operating assets and liabilities			(14)
Other changes in noncurrent assets and liabilities			355
Net cash provided by operating activities			37,008
Investing activities:
Utility plant expenditures			0
Proceeds from sale of non-utility properties			0
Change in affiliate advances			291
Collection of affiliate short-term borrowings			365
Life insurance benefits			0
Issuance of affiliate short-term borrowings			(2,365)
Collection of affiliate long-term debt			1,175
Purchase of life insurance contracts			0
Net cash used in investing activities			(534)
Financing Activities:
Short-term borrowings			44,100
Repayment of short-term borrowings			(20,615)
Change in affiliate advances			0
Proceeds from affiliate short-term borrowings			20,600
Repayment of affiliate short-term borrowings			(42,100)
Repayment of affiliate long-term debt			0
Issuance of long-term debt, net			0
Repayment of long-term debt			0
Repurchase of common stock			(744)
Advances and contributions in aid of construction			0
Refunds of advances for construction			0
Dividends paid to non-affiliates			(33,081)
Dividends paid to affiliates			0
Net cash provided by financing activities			(31,840)
Change in cash, cash equivalents, and restricted cash			4,634
Cash, cash equivalents, and restricted cash at beginning of year		5,216	582
Cash, cash equivalents, and restricted cash at end of year			5,216
Parent Company | Reportable Legal Entities
Operating activities:
Net income (loss)	65,584	72,940	48,675
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Equity earnings of subsidiaries	(64,748)	(72,487)	(48,158)
Dividends received from affiliates	36,043	34,563
Depreciation and amortization	94	94
Change in value of life insurance contracts	0	0
Stock-based compensation	3,141	3,118
(Gain) loss on sale of non-utility property	0	0	0
Changes in normalized deferred income taxes	0	0
Allowance for equity funds used during construction	0	0
Changes in operating assets and liabilities	(290)	184
Other changes in noncurrent assets and liabilities	(348)	254
Net cash provided by operating activities	39,476	38,666
Investing activities:
Utility plant expenditures	0	(4)
TCP settlement proceeds		0
Proceeds from sale of non-utility properties	0	0
Change in affiliate advances	(689)	172
Collection of affiliate short-term borrowings	20,000
Life insurance benefits	0	0
Issuance of affiliate short-term borrowings	(23,700)	(2,610)
Collection of affiliate long-term debt	1,635	1,356
Purchase of life insurance contracts	0	0
Net cash used in investing activities	(2,754)	(1,086)
Financing Activities:
Short-term borrowings	20,000	0
Repayment of short-term borrowings	(20,000)	(2,000)
Change in affiliate advances	17	0
Proceeds from affiliate short-term borrowings	20,000	0
Repayment of affiliate short-term borrowings	(20,000)
Repayment of affiliate long-term debt	0	0
Issuance of long-term debt, net	0
Repayment of long-term debt	0	0
Repurchase of common stock	(1,645)	(1,505)
Advances and contributions in aid of construction	0	0
Refunds of advances for construction	0	0
Dividends paid to non-affiliates	(36,043)	(34,563)
Dividends paid to affiliates	0	0
Net cash provided by financing activities	(37,671)	(38,068)
Change in cash, cash equivalents, and restricted cash	(949)	(488)
Cash, cash equivalents, and restricted cash at beginning of year	4,728	5,216
Cash, cash equivalents, and restricted cash at end of year	3,779	4,728	5,216
Cal Water
Operating activities:
Net income (loss)			45,316
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Equity earnings of subsidiaries			0
Dividends received from affiliates			0
Depreciation and amortization			60,572
Amortization of debt premium and expenses			871
Change in value of life insurance contracts			(1,026)
Stock-based compensation			0
(Gain) loss on sale of non-utility property			146
Write-off of capital costs			3,221
Changes in normalized deferred income taxes			26,818
Changes in operating assets and liabilities			6,534
Other changes in noncurrent assets and liabilities			4,645
Net cash provided by operating activities			147,097
Investing activities:
Utility plant expenditures			(224,378)
Proceeds from sale of non-utility properties			395
Change in affiliate advances			1,111
Collection of affiliate short-term borrowings			42,100
Life insurance benefits			495
Issuance of affiliate short-term borrowings			(20,600)
Collection of affiliate long-term debt			0
Purchase of life insurance contracts			(2,857)
Net cash used in investing activities			(203,734)
Financing Activities:
Short-term borrowings			101,000
Repayment of short-term borrowings			(61,000)
Change in affiliate advances			(128)
Proceeds from affiliate short-term borrowings			0
Repayment of affiliate short-term borrowings			0
Repayment of affiliate long-term debt			0
Issuance of long-term debt, net			49,823
Repayment of long-term debt			(6,548)
Repurchase of common stock			0
Advances and contributions in aid of construction			21,329
Refunds of advances for construction			(6,855)
Dividends paid to non-affiliates			0
Dividends paid to affiliates			(32,105)
Net cash provided by financing activities			65,516
Change in cash, cash equivalents, and restricted cash			8,879
Cash, cash equivalents, and restricted cash at beginning of year		13,595	4,716
Cash, cash equivalents, and restricted cash at end of year			13,595
Cal Water | Reportable Legal Entities
Operating activities:
Net income (loss)	61,905	70,071	45,316
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Equity earnings of subsidiaries	0	0	0
Dividends received from affiliates	0	0
Depreciation and amortization	80,442	74,041
Change in value of life insurance contracts	2,334	(3,058)
Stock-based compensation	0	0
(Gain) loss on sale of non-utility property	(50)	(663)	146
Changes in normalized deferred income taxes	20,909	21,087
Allowance for equity funds used during construction	(3,954)	(3,750)
Changes in operating assets and liabilities	16,943	(36,611)
Other changes in noncurrent assets and liabilities	(12,284)	13,101
Net cash provided by operating activities	166,245	134,218
Investing activities:
Utility plant expenditures	(261,456)	(252,055)
TCP settlement proceeds		56,004
Proceeds from sale of non-utility properties	59	666
Change in affiliate advances	19	(485)
Collection of affiliate short-term borrowings	0
Life insurance benefits	3,491	1,558
Issuance of affiliate short-term borrowings	0	0
Collection of affiliate long-term debt	0	0
Purchase of life insurance contracts	(4,925)	(5,605)
Net cash used in investing activities	(262,812)	(199,917)
Financing Activities:
Short-term borrowings	131,000	265,000
Repayment of short-term borrowings	(341,000)	(85,000)
Change in affiliate advances	(93)	41
Proceeds from affiliate short-term borrowings	0	0
Repayment of affiliate short-term borrowings	0
Repayment of affiliate long-term debt	0	0
Issuance of long-term debt, net	299,383
Repayment of long-term debt	(16,200)	(26,223)
Repurchase of common stock	0	0
Advances and contributions in aid of construction	18,218	21,075
Refunds of advances for construction	(7,279)	(8,373)
Dividends paid to non-affiliates	0	0
Dividends paid to affiliates	(34,624)	(33,015)
Net cash provided by financing activities	49,405	133,505
Change in cash, cash equivalents, and restricted cash	(47,162)	67,806
Cash, cash equivalents, and restricted cash at beginning of year	81,401	13,595
Cash, cash equivalents, and restricted cash at end of year	34,239	81,401	13,595
All Other Subsidiaries
Operating activities:
Net income (loss)			2,785
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Equity earnings of subsidiaries			0
Dividends received from affiliates			0
Depreciation and amortization			4,507
Amortization of debt premium and expenses			0
Change in value of life insurance contracts			0
Stock-based compensation			0
(Gain) loss on sale of non-utility property			0
Write-off of capital costs			0
Changes in normalized deferred income taxes			0
Changes in operating assets and liabilities			261
Other changes in noncurrent assets and liabilities			1,867
Net cash provided by operating activities			9,420
Investing activities:
Utility plant expenditures			(4,560)
Proceeds from sale of non-utility properties			0
Change in affiliate advances			(67)
Collection of affiliate short-term borrowings			0
Life insurance benefits			0
Issuance of affiliate short-term borrowings			0
Collection of affiliate long-term debt			0
Purchase of life insurance contracts			0
Net cash used in investing activities			(4,627)
Financing Activities:
Short-term borrowings			0
Repayment of short-term borrowings			0
Change in affiliate advances			(1,207)
Proceeds from affiliate short-term borrowings			2,365
Repayment of affiliate short-term borrowings			(365)
Repayment of affiliate long-term debt			(1,175)
Issuance of long-term debt, net			0
Repayment of long-term debt			(448)
Repurchase of common stock			0
Advances and contributions in aid of construction			119
Refunds of advances for construction			(30)
Dividends paid to non-affiliates			0
Dividends paid to affiliates			(976)
Net cash provided by financing activities			(1,717)
Change in cash, cash equivalents, and restricted cash			3,076
Cash, cash equivalents, and restricted cash at beginning of year		7,124	4,048
Cash, cash equivalents, and restricted cash at end of year			7,124
All Other Subsidiaries | Reportable Legal Entities
Operating activities:
Net income (loss)	2,863	2,362	2,785
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Equity earnings of subsidiaries	0	0	0
Dividends received from affiliates	0	0
Depreciation and amortization	5,258	4,548
Change in value of life insurance contracts	0	0
Stock-based compensation	0	0
(Gain) loss on sale of non-utility property	0	0	0
Changes in normalized deferred income taxes	0	0
Allowance for equity funds used during construction	0	0
Changes in operating assets and liabilities	(170)	38
Other changes in noncurrent assets and liabilities	1,390	2,573
Net cash provided by operating activities	9,341	9,521
Investing activities:
Utility plant expenditures	(10,251)	(7,135)
TCP settlement proceeds		0
Proceeds from sale of non-utility properties	0	0
Change in affiliate advances	53	(50)
Collection of affiliate short-term borrowings	0
Life insurance benefits	0	0
Issuance of affiliate short-term borrowings	0	0
Collection of affiliate long-term debt	0	0
Purchase of life insurance contracts	0	0
Net cash used in investing activities	(10,198)	(7,185)
Financing Activities:
Short-term borrowings	0	0
Repayment of short-term borrowings	0	0
Change in affiliate advances	693	322
Proceeds from affiliate short-term borrowings	3,700	2,610
Repayment of affiliate short-term borrowings	0
Repayment of affiliate long-term debt	(1,635)	(1,356)
Issuance of long-term debt, net	0
Repayment of long-term debt	(332)	(606)
Repurchase of common stock	0	0
Advances and contributions in aid of construction	394	294
Refunds of advances for construction	(18)	(5)
Dividends paid to non-affiliates	0	0
Dividends paid to affiliates	(1,419)	(1,548)
Net cash provided by financing activities	1,383	(289)
Change in cash, cash equivalents, and restricted cash	526	2,047
Cash, cash equivalents, and restricted cash at beginning of year	9,171	7,124
Cash, cash equivalents, and restricted cash at end of year	$ 9,697	$ 9,171	$ 7,124