Fair Value Measurement (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	$ 511,076		$ 511,076		$ 431,424
Unrealized loss on California Water Service Group stock	0	$ 0	0	$ (527)
Available for Sale Marketable Security, Shares Sold		82,340		100,000
Proceeds from sale of California Water Service Group stock		$ 3,398	0	$ 4,112
Fees Incurred on Sale of Available for Sale Securities		7		9
Gain on sale of California Water Service Group stock	0	191	0	104
Available for Sales Securities, Tax on Realized Gain		53		29
Debt and Equity Securities, Gain (Loss)		$ 138		$ 75
Significant Observable Inputs
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	$ 641,395		$ 641,395		$ 490,148

Available for Sale Marketable Security, Shares Sold

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Available for Sales Securities, Tax on Realized Gain

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Fees Incurred on Sale of Available for Sale Securities

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This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities.

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Amount of unrealized and realized gain (loss) on investment in debt and equity securities.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

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Amount of unrealized gain (loss) on investment in marketable security.

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The cash inflow associated with the sale of equity securities classified as available-for-sale securities.

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