Premises and Equipment - Summary of Premises and Equipment (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	$ 54,598	$ 53,385
Less: Accumulated depreciation and amortization	33,596	32,461
Total	21,002	20,924
Land [Member]
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	7,054	7,054
Buildings [Member]
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	23,487	23,176
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	1,126	1,124
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	$ 22,931	$ 22,031