Premises and Equipment Net - Components of Premises and Equipment Included in Balance Sheets (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Premises and equipment	$ 24,739	$ 22,644
Less accumulated depreciation	(12,857)	(12,024)
Premises and equipment, net	11,882	10,620
Land and Improvements
Property, Plant and Equipment [Line Items]
Premises and equipment	2,004	1,998
Buildings and Improvements
Property, Plant and Equipment [Line Items]
Premises and equipment	13,032	11,764
Furniture and Equipment
Property, Plant and Equipment [Line Items]
Premises and equipment	$ 9,703	$ 8,882