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Summary of Significant Accounting Policies (Investment in California Water Service Group) (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Public Utilities, General Disclosures [Line Items] |  |  |
Available for Sale Marketable Security, Shares Held | 0 |  |
Available for Sale Marketable Security, Shares Sold | 100,000 |  | 159,151
Proceeds from Sale of Debt Securities, Available-for-sale | $ 4,510 |  |
Proceeds from sale of California Water Service Group stock | 4,112 | $ 0 | $ 4,509
Fees Incurred on Sale of Available for Sale Securities | 9 |  | 20
Gain on sale of California Water Service Group stock | 104 | 0 | 3,197
Available for Sales Securities, Tax on Realized Gain | 29 |  | 1,303
Debt and Equity Securities, Gain (Loss) | 75 |  | 1,894
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax | 0 | 0 | $ 1,742
Quoted Prices in Active Markets for Identical Assets (Level 1) |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Available-for-sale Securities | $ 0 | $ 4,535 |

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