Premises and Equipment - Summary of Premises and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 107,676	$ 102,454
Less: Accumulated depreciation	62,720	54,471
Property, plant and equipment, net	44,956	47,983
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,758	2,758
Buildings
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	6,179	6,155
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	49,704	48,573
Furniture and equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 49,035	$ 44,968