CONDENSED CONSOLIDATING FINANCIAL STATEMENTS (Details 4) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities:
Net income (loss)	$ 67,181	$ 48,675	$ 45,017
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	78,592	65,203	63,182
Amortization of debt premium and expenses	920	871	825
Change in value of life insurance contracts	(3,058)	(1,026)	218
Stock-based compensation	3,118	2,849	2,578
(Gain) loss on sale of non-utility property	(663)	146	(315)
Write-off of capital costs	1,293	3,221	0
Changes in normalized deferred income taxes	21,087	26,818	24,393
Allowance for equity funds used during construction	(3,750)	0	0
Changes in operating assets and liabilities	(36,389)	6,781	(1,877)
Other changes in noncurrent assets and liabilities	21,724	6,906	11,773
Net cash provided by operating activities	147,842	160,444	144,969
Investing activities:
Utility plant expenditures	(259,194)	(228,938)	(176,833)
TCP settlement proceeds	56,004	0	0
Proceeds from sale of non-utility properties	666	395	319
Investment in affiliates			0
Change in affiliate advances	0	0	0
Collection of affiliate short-term borrowings		0	0
Life insurance benefits	1,558	495	0
Issuance of affiliate short-term borrowings	0	0	0
Collection of affiliate long-term debt	0	0	0
Purchase of life insurance contracts	(5,605)	(2,857)	(2,032)
Change in restricted cash	(81)	66	288
Net cash used in investing activities	(206,652)	(230,839)	(178,258)
Financing Activities:
Short-term borrowings	265,000	145,100	94,303
Repayment of short-term borrowings	(87,000)	(81,615)	(141,000)
Investment from affiliates			0
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	0	49,823	99,343
Repayment of long-term debt	(26,829)	(6,996)	(7,003)
Repurchase of common stock	(1,505)	(744)	(338)
Advances and contributions in aid of construction	21,369	21,448	16,026
Refunds of advances for construction	(8,378)	(6,885)	(6,726)
Dividends paid to non-affiliates	(34,563)	(33,081)	(32,066)
Dividends paid to affiliates	0	0	0
Net cash provided by financing activities	128,094	87,050	22,539
Change in cash and cash equivalents	69,284	16,655	(10,750)
Cash and cash equivalents at beginning of year	25,492	8,837	19,587
Cash and cash equivalents at end of year	94,776	25,492	8,837
Consolidating Adjustments
Operating activities:
Net income (loss)	(66,674)	(48,101)	(44,456)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Equity earnings of subsidiaries	66,728	48,158	44,516
Dividends received from affiliates	(34,563)	(33,081)	(32,066)
Depreciation and amortization	(91)	(96)	(101)
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
Changes in operating assets and liabilities	0	0	(94)
Other changes in noncurrent assets and liabilities	37	39	135
Net cash provided by operating activities	(34,563)	(33,081)	(32,066)
Investing activities:
Utility plant expenditures	0	0	0
TCP settlement proceeds	0
Proceeds from sale of non-utility properties	0	0	0
Investment in affiliates			1,000
Change in affiliate advances	363	(1,335)	1,235
Collection of affiliate short-term borrowings		(42,465)	(3,000)
Life insurance benefits	0	0
Issuance of affiliate short-term borrowings	2,610	22,965	24,780
Collection of affiliate long-term debt	(1,356)	(1,175)	(1,007)
Purchase of life insurance contracts	0	0	0
Change in restricted cash	0	0	0
Net cash used in investing activities	1,617	(22,010)	23,008
Financing Activities:
Short-term borrowings	0	0	0
Repayment of short-term borrowings	0	0	0
Investment from affiliates			(1,000)
Change in affiliate advances	(363)	1,335	(1,235)
Proceeds from affiliate short-term borrowings	(2,610)	(22,965)	(24,780)
Repayment of affiliate short-term borrowings		42,465	3,000
Repayment of affiliate long-term debt	1,356	1,175	1,007
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	34,563	33,081	32,066
Net cash provided by financing activities	32,946	55,091	9,058
Change in cash and cash equivalents	0	0	0
Cash and cash equivalents at beginning of year	0	0	0
Cash and cash equivalents at end of year	0	0	0
Parent Company
Operating activities:
Net income (loss)	67,181	48,675	45,017
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Equity earnings of subsidiaries	(66,728)	(48,158)	(44,516)
Dividends received from affiliates	34,563	33,081	32,066
Depreciation and amortization	94	220	228
Amortization of debt premium and expenses		0
Change in value of life insurance contracts	0	0	0
Stock-based compensation	3,118	2,849	2,578
(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
Changes in operating assets and liabilities	184	(14)	(758)
Other changes in noncurrent assets and liabilities	254	355	1,774
Net cash provided by operating activities	38,666	37,008	36,389
Investing activities:
Utility plant expenditures	(4)	0	0
TCP settlement proceeds	0
Proceeds from sale of non-utility properties	0	0	0
Investment in affiliates			(1,000)
Change in affiliate advances	172	291	(239)
Collection of affiliate short-term borrowings		365	3,000
Life insurance benefits	0	0
Issuance of affiliate short-term borrowings	(2,610)	(2,365)	(3,280)
Collection of affiliate long-term debt	1,356	1,175	1,007
Purchase of life insurance contracts	0	0	0
Change in restricted cash	0	0	0
Net cash used in investing activities	(1,086)	(534)	(512)
Financing Activities:
Short-term borrowings	0	44,100	15,101
Repayment of short-term borrowings	(2,000)	(20,615)	(43,600)
Investment from affiliates			0
Change in affiliate advances	0	0	0
Proceeds from affiliate short-term borrowings	0	20,600	21,500
Repayment of affiliate short-term borrowings		(42,100)	0
Repayment of affiliate long-term debt	0	0	0
Issuance of long-term debt, net		0	0
Repayment of long-term debt	0	0	0
Repurchase of common stock	(1,505)	(744)	(338)
Advances and contributions in aid of construction	0	0	0
Refunds of advances for construction	0	0	0
Dividends paid to non-affiliates	(34,563)	(33,081)	(32,066)
Dividends paid to affiliates	0	0	0
Net cash provided by financing activities	(38,068)	(31,840)	(39,403)
Change in cash and cash equivalents	(488)	4,634	(3,526)
Cash and cash equivalents at beginning of year	5,216	582	4,108
Cash and cash equivalents at end of year	4,728	5,216	582
Cal Water
Operating activities:
Net income (loss)	64,312	45,316	44,056
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	74,041	60,572	58,385
Amortization of debt premium and expenses		871
Change in value of life insurance contracts	(3,058)	(1,026)	218
Stock-based compensation	0	0	0
(Gain) loss on sale of non-utility property	(663)	146	(315)
Write-off of capital costs		3,221
Changes in normalized deferred income taxes	21,087	26,818	24,393
Allowance for equity funds used during construction	(3,750)
Changes in operating assets and liabilities	(36,611)	6,534	(6,417)
Other changes in noncurrent assets and liabilities	18,860	4,645	14,807
Net cash provided by operating activities	134,218	147,097	135,127
Investing activities:
Utility plant expenditures	(252,055)	(224,378)	(171,645)
TCP settlement proceeds	56,004
Proceeds from sale of non-utility properties	666	395	319
Investment in affiliates			0
Change in affiliate advances	(485)	1,111	(1,111)
Collection of affiliate short-term borrowings		42,100	0
Life insurance benefits	1,558	495
Issuance of affiliate short-term borrowings	0	(20,600)	(21,500)
Collection of affiliate long-term debt	0	0	0
Purchase of life insurance contracts	(5,605)	(2,857)	(2,032)
Change in restricted cash	(81)	66	288
Net cash used in investing activities	(199,998)	(203,668)	(195,681)
Financing Activities:
Short-term borrowings	265,000	101,000	79,202
Repayment of short-term borrowings	(85,000)	(61,000)	(97,400)
Investment from affiliates			0
Change in affiliate advances	41	(128)	397
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		49,823	99,293
Repayment of long-term debt	(26,223)	(6,548)	(6,528)
Repurchase of common stock	0	0	0
Advances and contributions in aid of construction	21,075	21,329	14,195
Refunds of advances for construction	(8,373)	(6,855)	(6,681)
Dividends paid to non-affiliates	0	0	0
Dividends paid to affiliates	(33,015)	(32,105)	(31,583)
Net cash provided by financing activities	133,505	65,516	50,895
Change in cash and cash equivalents	67,725	8,945	(9,659)
Cash and cash equivalents at beginning of year	13,215	4,270	13,929
Cash and cash equivalents at end of year	80,940	13,215	4,270
All Other Subsidiaries
Operating activities:
Net income (loss)	2,362	2,785	400
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	4,548	4,507	4,670
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
Changes in operating assets and liabilities	38	261	5,392
Other changes in noncurrent assets and liabilities	2,573	1,867	(4,943)
Net cash provided by operating activities	9,521	9,420	5,519
Investing activities:
Utility plant expenditures	(7,135)	(4,560)	(5,188)
TCP settlement proceeds	0
Proceeds from sale of non-utility properties	0	0	0
Investment in affiliates			0
Change in affiliate advances	(50)	(67)	115
Collection of affiliate short-term borrowings		0	0
Life insurance benefits	0	0
Issuance of affiliate short-term borrowings	0	0	0
Collection of affiliate long-term debt	0	0	0
Purchase of life insurance contracts	0	0	0
Change in restricted cash	0	0	0
Net cash used in investing activities	(7,185)	(4,627)	(5,073)
Financing Activities:
Short-term borrowings	0	0	0
Repayment of short-term borrowings	0	0	0
Investment from affiliates			1,000
Change in affiliate advances	322	(1,207)	838
Proceeds from affiliate short-term borrowings	2,610	2,365	3,280
Repayment of affiliate short-term borrowings		(365)	(3,000)
Repayment of affiliate long-term debt	(1,356)	(1,175)	(1,007)
Issuance of long-term debt, net		0	50
Repayment of long-term debt	(606)	(448)	(475)
Repurchase of common stock	0	0	0
Advances and contributions in aid of construction	294	119	1,831
Refunds of advances for construction	(5)	(30)	(45)
Dividends paid to non-affiliates	0	0	0
Dividends paid to affiliates	(1,548)	(976)	(483)
Net cash provided by financing activities	(289)	(1,717)	1,989
Change in cash and cash equivalents	2,047	3,076	2,435
Cash and cash equivalents at beginning of year	7,061	3,985	1,550
Cash and cash equivalents at end of year	$ 9,108	$ 7,061	$ 3,985