Commitments and Contingencies - Summary of Financial Instruments Outstanding (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Commitments to grant loans	$ 518,934	$ 355,558
Unfunded commitments under lines of credit	5,051,175	4,899,930
Commercial and standby letters of credit	183,031	163,560
Reserve for unfunded lending commitments	$ 10,462	$ 11,241	$ 13,826	$ 14,145