Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands |
Mar. 31, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Statement of Financial Position [Abstract] | ||
| Interest bearing deposits, banks | $ 9,484 | $ 19,826 |
| Held-to-maturity securities, fair values | $ 1,005,502 | $ 1,023,784 |
| Preferred stock, no par value | ||
| Preferred stock, shares authorized | 1,000,000 | 1,000,000 |
| Preferred stock, shares outstanding | 0 | 0 |
| Common stock, par value | $ 2.0833 | $ 2.0833 |
| Common stock, shares authorized | 100,000,000 | 100,000,000 |
| Common stock, shares issued | 44,060,957 | 44,043,244 |
| Common stock, shares outstanding | 44,060,957 | 44,043,244 |
| Treasury stock, shares | 0 | 0 |