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Significant Accounting Policies and Basis of Presentation - Narrative (Details) - USD ($) $ in Thousands | Jan. 01, 2018 | Jun. 30, 2018 | Dec. 31, 2017
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New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Retained earnings |  | $ 299,990 | $ 258,076
Accounting Standards Update 2018-02 |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Cumulative effect of new accounting principle in period of adoption |  |  | 0
Accounting Standards Update 2016-01 |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Cumulative effect of new accounting principle in period of adoption |  |  | $ 0
Net unrealized gain | $ 1,041 |  |
Accumulated Other Comprehensive Loss | Accounting Standards Update 2018-02 |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Cumulative effect of new accounting principle in period of adoption | (298) |  |
Accumulated Other Comprehensive Loss | Accounting Standards Update 2016-01 |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Cumulative effect of new accounting principle in period of adoption | (1,041) |  |
Retained Earnings | Accounting Standards Update 2018-02 |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Cumulative effect of new accounting principle in period of adoption | 298 |  |
Retained Earnings | Accounting Standards Update 2016-01 |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Cumulative effect of new accounting principle in period of adoption | $ 1,041 |  |

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