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Stockholders' Equity - Summary of Preferred and Common Stock (Parenthetical) (Details) | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016
Series B 7.5% Fixed Non-Cumulative Perpetual Preferred Stock |  |
Class Of Stock [Line Items] |  |
Preferred stock, dividend rate, percentage | 7.50% | 7.50%

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- Details
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