Commitments and Contingent Liabilities - Commitments to Extend Credit, Guarantees and Various Letters of Credit Outstanding (Detail) - USD ($) $ in Thousands |
Mar. 31, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Commitments and Contingencies Disclosure [Abstract] | ||
| Lines of credit | $ 1,464,970 | $ 1,452,697 |
| Loans approved but not closed | 358,367 | 245,644 |
| Overdraft limits | 124,752 | 126,671 |
| Letters of credit | 31,947 | 31,951 |
| Contingent obligations and other guarantees | $ 6,796 | $ 6,700 |