Commitments and Contingent Liabilities - Commitments to Extend Credit, Guarantees and Various Letters of Credit Outstanding (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Commitments And Contingencies Disclosure [Abstract]
Lines of credit	$ 1,909,282	$ 1,894,030
Loans approved but not closed	299,081	258,778
Overdraft limits	152,207	153,572
Letters of credit	45,960	42,841
Contingent obligations and other guarantees	$ 48,654	$ 61,509