Premises and Equipment - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Depreciation expense of premises and equipment	$ 8,329	$ 8,557	$ 7,477
Depreciation expense of premises and equipment for 2016			7,600
Rent expense of operating leases	$ 12,900	$ 13,000	$ 11,500
Minimum
Property, Plant and Equipment [Line Items]
Operating leases, lease terms	1 year
Maximum
Property, Plant and Equipment [Line Items]
Operating leases, lease terms	25 years
Computer Equipment
Property, Plant and Equipment [Line Items]
Useful life	3 years
Furniture and equipment
Property, Plant and Equipment [Line Items]
Useful life	5 years
Building Renovations
Property, Plant and Equipment [Line Items]
Useful life	10 years