Deposits - Additional Information (Details) - USD ($) $ in Millions |
Dec. 31, 2017 |
Dec. 31, 2016 |
|---|---|---|
| Deposits [Abstract] | ||
| Certificates of deposits of $250,000 or more, maturities within one year | $ 229.7 | $ 182.8 |
| Certificates of deposits of $250,000 or more, maturities after one year | 58.5 | 7.1 |
| Certificates of deposits of $250,000 or more, total | 288.2 | 189.9 |
| Certificates of deposit of less than $ 250,000, maturities within one year | 542.7 | 416.3 |
| Certificates of deposit of less than $ 250,000, maturities after one year | 69.9 | 23.2 |
| Certificates of deposit of less than $250,000, total | $ 612.6 | $ 439.5 |