Securities - Summary of AFS Securities Portfolio (Details) - USD ($) $ in Thousands |
Sep. 30, 2017 |
Dec. 31, 2016 |
|---|---|---|
| Schedule Of Available For Sale Securities [Line Items] | ||
| Amortized cost | $ 475,889 | $ 518,491 |
| Gross Unrealized gains | 2,253 | 871 |
| Gross Unrealized losses | (6,640) | (9,784) |
| Estimated Fair Value | 471,502 | 509,578 |
| U.S. Treasury Securities | ||
| Schedule Of Available For Sale Securities [Line Items] | ||
| Amortized cost | 499 | 300 |
| Gross Unrealized losses | (4) | (3) |
| Estimated Fair Value | 495 | 297 |
| Agency Mortgage-backed Securities | ||
| Schedule Of Available For Sale Securities [Line Items] | ||
| Amortized cost | 436,415 | 476,163 |
| Gross Unrealized gains | 497 | 160 |
| Gross Unrealized losses | (4,464) | (7,414) |
| Estimated Fair Value | 432,448 | 468,909 |
| Beneficial interests in FHLMC securitization | ||
| Schedule Of Available For Sale Securities [Line Items] | ||
| Amortized cost | 38,975 | 42,028 |
| Gross Unrealized gains | 1,756 | 711 |
| Gross Unrealized losses | (2,172) | (2,367) |
| Estimated Fair Value | $ 38,559 | $ 40,372 |