Premises and Equipment - Summary of Premises and Equipment (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Land	$ 10,471	$ 10,626
Buildings and building improvements	47,006	46,985
Leasehold improvements	12,880	12,953
Furniture, fixtures and equipment	27,858	26,923
Premises and equipment, gross	98,215	97,487
Less accumulated depreciation and amortization	49,040	47,174
Premises and equipment	$ 49,175	$ 50,313
Buildings and building improvements | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives	10 years
Buildings and building improvements | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives	50 years
Leasehold improvements | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives	10 years
Leasehold improvements | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives	25 years
Furniture, fixtures and equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives	2 years
Furniture, fixtures and equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives	30 years