Commitments and Contingencies - Summary of Financial Instruments as of the Dates Indicated (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Commitments to extend credit
Disclosure Of Financial Instruments Indicated [Line Items]
Contractual obligation	$ 3,959,011	$ 3,818,952
Standby letters of credit
Disclosure Of Financial Instruments Indicated [Line Items]
Contractual obligation	63,986	60,221
Forward commitments to sell loans
Disclosure Of Financial Instruments Indicated [Line Items]
Contractual obligation	$ 35,564	$ 41,160