Commitments and Contingent Liabilities - Commitments to Extend Credit, Guarantees and Various Letters of Credit Outstanding (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Commitments And Contingencies Disclosure [Abstract]
Lines of credit	$ 2,418,066	$ 2,469,676
Loans approved but not closed	541,038	504,623
Overdraft limits	154,481	149,519
Letters of credit	59,272	57,205
Contingent obligations and other guarantees	$ 76,170	$ 81,551