Premises and Equipment - Summary of Premises and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	$ 66,709	$ 64,132
Less: Accumulated depreciation and amortization	44,779	42,038
Total	21,930	22,094
Land [Member]
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	7,427	7,427
Buildings [Member]
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	26,151	25,814
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	1,865	1,857
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	$ 31,266	$ 29,034