Derivative Instruments and Hedging Activities - Amount of Gain or Loss Recognized in Income on Derivatives (Detail) (Not Designated as Hedging Instruments [Member], USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Total Derivative Gain (Loss)	$ 36	$ (474)	$ 371
Interest Rate Swap Contracts-Commercial Loans [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total Derivative Gain (Loss)	(24)	(174)	101
Interest Rate Lock Commitments-Mortgage Loans [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total Derivative Gain (Loss)	150	(382)	223
Forward Sale Contracts-Mortgage Loans [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total Derivative Gain (Loss)	$ (90)	$ 82	$ 47