Premises and Equipment - Summary of Premises and Equipment (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 186,253	$ 181,814
Less: Accumulated depreciation	89,697	77,349
Property, plant and equipment, net	96,556	104,465
Depreciation expense of premises and equipment	14,999	15,852	$ 8,329
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	20,209	20,209
Buildings
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	35,343	34,637
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	63,365	62,523
Furniture and equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	67,336	64,445
Land, Buildings, Leasehold Improvements, Furniture and Equipment
Property, Plant and Equipment [Line Items]
Depreciation expense of premises and equipment	$ 14,300	$ 15,000	$ 8,300