Commitments and Contingent Liabilities - Commitments to Extend Credit, Guarantees and Various Letters of Credit Outstanding (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Commitments And Contingencies Disclosure [Abstract]
Lines of credit	$ 2,013,085	$ 1,894,030
Loans approved but not closed	391,885	258,778
Overdraft limits	150,684	153,572
Letters of credit	44,370	42,841
Contingent obligations and other guarantees	$ 68,450	$ 61,509