Commitments and Contingent Liabilities - Commitments to Extend Credit, Guarantees and Various Letters of Credit Outstanding (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Lines of credit	$ 1,418,329	$ 1,159,769
Loans approved but not closed	185,254	234,599
Overdraft limits	126,517	106,252
Letters of credit	32,907	27,408
Contingent obligations to purchase loans funded by other entities	$ 13,036	$ 18,079