Commitments and Contingent Liabilities - Commitments to Extend Credit, Guarantees and Various Letters of Credit Outstanding (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Lines of credit	$ 1,404,726	$ 1,159,769
Loans approved but not closed	150,864	234,599
Overdraft limits	127,277	106,252
Letters of credit	26,544	27,408
Contingent obligations to purchase loans funded by other entities	$ 17,324	$ 18,079