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Summary of Significant Accounting Policies - Accounting Standards (Details) $ in Thousands | Jan. 01, 2019 USD ($) | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) equity_security
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Debt Securities, Available-for-sale [Line Items] |  |  |
Number of equity securities | equity_security |  |  | 1
Debt Securities, Available-for-sale |  | $ 88,179 | $ 93,383
Equity Funds [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale |  | $ 0 | $ 499
Accounting Standards Update 2016-02 [Member] | Pro Forma [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Operating Lease, Right-of-Use Asset | $ 6,700 |  |

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