Premises and Equipment (Composition of Premises and Equipment) (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Premises and equipment	$ 54,168	$ 52,320
Less accumulated depreciation	(23,287)	(25,160)
Premises and equipment, net	30,881	27,160
Land [Member]
Property, Plant and Equipment [Line Items]
Premises and equipment	7,035	7,383
Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Premises and equipment	1,203	1,201
Premises [Member]
Property, Plant and Equipment [Line Items]
Premises and equipment	25,150	25,696
Furniture and Equipment [Member]
Property, Plant and Equipment [Line Items]
Premises and equipment	20,246	17,506
Capital Lease [Member]
Property, Plant and Equipment [Line Items]
Premises and equipment	$ 534	$ 534