Commitments and Contingencies - Summary of Financial Instruments Outstanding (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Commitments to extend credit	$ 806,164	$ 642,162
Unfunded commitments under lines of credit	7,240,808	6,883,963
Commercial and standby letters of credit	327,336	240,436
Reserve for unfunded lending commitments	$ 16,637	$ 14,830	$ 13,208	$ 11,241