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Significant Accounting Policies Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | ---
Jun. 30, 2019 | Dec. 31, 2019 | Jan. 01, 2019 | Dec. 31, 2018 | Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |
Operating Lease, Right-of-Use Asset | $ 284,500 |  | $ 170,500 |  |
Operating Lease, Liability | 291,700 |  | $ 174,400 |  |
Recognition of right of use asset related to the new corporate headquarters facility | 121,700 |  |  |  |
Recognition of operating lease liability related to the new corporate headquarters facility | $ 121,700 |  |  |  |
Cumulative effect of new accounting principle in period of adoption |  |  |  | $ (12,611) | $ (2,285)
Retained Earnings [Member] |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |
Cumulative effect of new accounting principle in period of adoption |  |  |  | $ (12,611) | $ (2,285)
Two Thousand And Nineteen [Member] | Scenario, Forecast [Member] |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |
Additional premium amortization expense on securities |  | $ 5,200 |  |  |

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