Securities - Additional Information (Details) |
Dec. 31, 2017 |
Dec. 31, 2016 |
|---|---|---|
| Schedule Of Available For Sale Securities [Line Items] | ||
| Weighted average yield, total | 5.13% | 0.90% |
| Agency Mortgage-backed Securities | ||
| Schedule Of Available For Sale Securities [Line Items] | ||
| Weighted average yield, total | 2.55% | 2.58% |