Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Allowance for loan losses	$ 44,859	$ 12,788	$ 11,207
Compensation and benefits	6,894	7,144	5,851
Security gains	2,113	3,031	3,707
Non-accrual interest income	1,135	1,297	1,388
Tax credit carryforwards		149
Net operating loss carryforwards	5,472	6,923	4,854
Fair value adjustments on securities available-for-sale			6,345
Lease accrual	13,530	13,787
Other	5,441	2,314	2,125
Gross deferred tax assets	79,444	47,433	35,477
Deferred tax liabilities:
Depreciation and amortization	(3,414)	(4,014)	(1,020)
Accretion on securities	(274)	(339)	(461)
Deferred fees and costs	(3,018)	(2,388)	(1,641)
Purchase accounting adjustments	(8,669)	(2,787)	(1,003)
Fair value adjustments on securities available-for-sale	(14,865)	(5,749)
Partnership adjustments	(555)	(521)	(680)
Lease - right of use assets	(12,438)	(13,064)
Other	(168)	(40)	(367)
Gross deferred tax liabilities	(43,401)	(28,902)	(5,172)
Net deferred tax assets	$ 36,043	$ 18,531	$ 30,305