Commitments and Contingencies - Summary of Financial Instruments Outstanding (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments to extend credit	$ 677,297	$ 806,164
Unfunded commitments under lines of credit	7,006,974	7,240,808
Commercial and standby letters of credit	277,415	327,336
Reserve for unfunded lending commitments	$ 18,302	$ 16,637