Commitment and Contingencies - Off Balance Sheet Arrangements of Bank (Details) - USD ($) $ in Thousands |
Dec. 31, 2017 |
Dec. 31, 2016 |
|---|---|---|
| Commitments And Contingencies Disclosure [Abstract] | ||
| Commitments to fund new loans | $ 44,561 | $ 43,006 |
| Commitments to fund under existing loans, lines of credit | 211,712 | 211,745 |
| Commitments under standby letters of credit | $ 2,352 | $ 4,830 |