Condensed Consolidating Financial Statements - Condensed Consolidating Statement of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Operating activities:
Net income	$ 16,996	$ (7,640)	$ 14,805	$ (762)	$ 9,356	$ 14,043
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					45,744	42,582
Change in value of life insurance contracts					(3,147)	817
Allowance for equity funds used during construction	(1,686)		(710)		(3,219)	(1,621)
Changes in operating assets and liabilities:
Changes in operating assets and liabilities					(16,837)	(16,389)
Other changes in noncurrent assets and liabilities					11,494	10,139
Net cash provided by operating activities					43,391	49,571
Investing activities:
Utility plant expenditures					(121,936)	(133,900)
Changes in affiliate advances					0	0
Issuance of affiliate short-term borrowings					0	0
Reduction of affiliates long-term debt					0	0
Life insurance proceeds					0	2,054
Purchase of life insurance contracts					0	(2,054)
Net cash used in investing activities					(121,936)	(133,900)
Financing Activities:
Short-term borrowings					190,000	111,000
Repayment of short-term borrowings					(90,000)	(61,000)
Proceeds from affiliate short-term borrowings					0	0
Changes in affiliate advances					0	0
Repayment of affiliates long-term borrowings					0	0
Issuance of long-term debt, net of expenses					398,442	0
Repayment of long-term debt					(401,358)	(12,264)
Advances and contributions in aid of construction					12,755	8,385
Refunds of advances for construction					(3,555)	(3,498)
Repurchase of common stock					(2,203)	(1,364)
Issuance of common stock					829	0
Dividends paid to non-affiliates					(19,000)	(18,017)
Dividends paid to affiliates					0	0
Net cash provided by financing activities					85,910	23,242
Change in cash, cash equivalents, and restricted cash					7,365	(61,087)
Cash, cash equivalents, and restricted cash at beginning of period		47,715		95,352	47,715	95,352
Cash, cash equivalents, and restricted cash at end of period	55,080		34,265		55,080	34,265
Consolidating Adjustments
Operating activities:
Net income	(16,909)		(14,700)		(9,160)	(13,743)
Adjustments to reconcile net income to net cash provided by operating activities:
Equity earnings of subsidiaries	16,923		14,717		9,189	13,775
Dividends received from affiliates					(19,000)	(18,017)
Depreciation and amortization					(41)	(43)
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					12	11
Net cash provided by operating activities					(19,000)	(18,017)
Investing activities:
Utility plant expenditures					0	0
Changes in affiliate advances					(1,238)	(3,187)
Issuance of affiliate short-term borrowings					4,300	3,700
Reduction of affiliates long-term debt					(848)	(818)
Life insurance proceeds						0
Purchase of life insurance contracts						0
Net cash used in investing activities					2,214	(305)
Financing Activities:
Short-term borrowings					0	0
Repayment of short-term borrowings					0	0
Proceeds from affiliate short-term borrowings					(4,300)	(3,700)
Changes in affiliate advances					1,238	3,187
Repayment of affiliates long-term borrowings					848	818
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
Dividends paid to non-affiliates					0	0
Dividends paid to affiliates					19,000	18,017
Net cash provided by financing activities					16,786	18,322
Change in cash, cash equivalents, and restricted cash					0	0
Cash, cash equivalents, and restricted cash at beginning of period		0		0	0	0
Cash, cash equivalents, and restricted cash at end of period	0		0		0	0
Parent Company | Reportable Legal Entities
Operating activities:
Net income	16,996		14,805		9,356	14,043
Adjustments to reconcile net income to net cash provided by operating activities:
Equity earnings of subsidiaries	(16,923)		(14,717)		(9,189)	(13,775)
Dividends received from affiliates					19,000	18,017
Depreciation and amortization					47	47
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					63	(417)
Other changes in noncurrent assets and liabilities					3,763	1,610
Net cash provided by operating activities					23,040	19,525
Investing activities:
Utility plant expenditures					0	0
Changes in affiliate advances					(1,453)	58
Issuance of affiliate short-term borrowings					(4,300)	(3,700)
Reduction of affiliates long-term debt					848	818
Life insurance proceeds						0
Purchase of life insurance contracts						0
Net cash used in investing activities					(4,905)	(2,824)
Financing Activities:
Short-term borrowings					0	0
Repayment of short-term borrowings					0	0
Proceeds from affiliate short-term borrowings					0	0
Changes in affiliate advances					(17)	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					(2,203)	(1,364)
Issuance of common stock					829
Dividends paid to non-affiliates					(19,000)	(18,017)
Dividends paid to affiliates					0	0
Net cash provided by financing activities					(20,391)	(19,381)
Change in cash, cash equivalents, and restricted cash					(2,256)	(2,680)
Cash, cash equivalents, and restricted cash at beginning of period		3,779		4,728	3,779	4,728
Cash, cash equivalents, and restricted cash at end of period	1,523		2,048		1,523	2,048
Cal Water | Reportable Legal Entities
Operating activities:
Net income	15,315		13,679		7,374	12,742
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					42,717	40,146
Change in value of life insurance contracts					(3,147)	817
Allowance for equity funds used during construction	(1,686)		(710)		(3,219)	(1,621)
Changes in operating assets and liabilities:
Changes in operating assets and liabilities					(16,581)	(16,439)
Other changes in noncurrent assets and liabilities					6,289	8,087
Net cash provided by operating activities					33,433	43,732
Investing activities:
Utility plant expenditures					(116,384)	(128,683)
Changes in affiliate advances					2,856	3,323
Issuance of affiliate short-term borrowings					0	0
Reduction of affiliates long-term debt					0	0
Life insurance proceeds						2,054
Purchase of life insurance contracts						(2,054)
Net cash used in investing activities					(113,528)	(125,360)
Financing Activities:
Short-term borrowings					190,000	111,000
Repayment of short-term borrowings					(90,000)	(61,000)
Proceeds from affiliate short-term borrowings					0	0
Changes in affiliate advances					2,430	129
Repayment of affiliates long-term borrowings					0	0
Issuance of long-term debt, net of expenses					398,442
Repayment of long-term debt					(401,256)	(12,136)
Advances and contributions in aid of construction					12,679	8,029
Refunds of advances for construction					(3,554)	(3,489)
Repurchase of common stock					0	0
Issuance of common stock					0
Dividends paid to non-affiliates					0	0
Dividends paid to affiliates					(18,348)	(17,330)
Net cash provided by financing activities					90,393	25,203
Change in cash, cash equivalents, and restricted cash					10,298	(56,425)
Cash, cash equivalents, and restricted cash at beginning of period		34,238		81,453	34,238	81,453
Cash, cash equivalents, and restricted cash at end of period	44,536		25,028		44,536	25,028
All Other Subsidiaries | Reportable Legal Entities
Operating activities:
Net income	1,594		1,021		1,786	1,001
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					3,021	2,432
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					(319)	467
Other changes in noncurrent assets and liabilities					1,430	431
Net cash provided by operating activities					5,918	4,331
Investing activities:
Utility plant expenditures					(5,552)	(5,217)
Changes in affiliate advances					(165)	(194)
Issuance of affiliate short-term borrowings					0	0
Reduction of affiliates long-term debt					0	0
Life insurance proceeds						0
Purchase of life insurance contracts						0
Net cash used in investing activities					(5,717)	(5,411)
Financing Activities:
Short-term borrowings					0	0
Repayment of short-term borrowings					0	0
Proceeds from affiliate short-term borrowings					4,300	3,700
Changes in affiliate advances					(3,651)	(3,316)
Repayment of affiliates long-term borrowings					(848)	(818)
Issuance of long-term debt, net of expenses					0
Repayment of long-term debt					(102)	(128)
Advances and contributions in aid of construction					76	356
Refunds of advances for construction					(1)	(9)
Repurchase of common stock					0	0
Issuance of common stock					0
Dividends paid to non-affiliates					0	0
Dividends paid to affiliates					(652)	(687)
Net cash provided by financing activities					(878)	(902)
Change in cash, cash equivalents, and restricted cash					(677)	(1,982)
Cash, cash equivalents, and restricted cash at beginning of period		$ 9,698		$ 9,171	9,698	9,171
Cash, cash equivalents, and restricted cash at end of period	$ 9,021		$ 7,189		$ 9,021	$ 7,189