Derivative Instruments and Hedging Activities - Value of Derivative Assets and Derivative Liabilities (Detail) (Not Designated as Hedging Instruments [Member], USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Derivatives not Designated as Hedging Instruments
Fair value, Derivatives (included in Other Assets)	$ 12,981	$ 13,698
Fair value, Derivatives (included in Other Liabilities)	12,953	13,647
Other Assets [Member] | Interest Rate Swap Contracts-Commercial Loans [Member]
Derivatives not Designated as Hedging Instruments
Fair value, Derivatives (included in Other Assets)	12,981	13,698
Notional amount, Derivatives (included in Other Assets)	245,152	261,754
Other Assets [Member] | Interest Rate Lock Commitments-Mortgage Loans [Member]
Derivatives not Designated as Hedging Instruments
Fair value, Derivatives (included in Other Assets)	235	85
Notional amount, Derivatives (included in Other Assets)	8,822	3,989
Other Assets [Member] | Forward Sale Contracts-Mortgage Loans [Member]
Derivatives not Designated as Hedging Instruments
Fair value, Derivatives (included in Other Assets)	0	34
Notional amount, Derivatives (included in Other Assets)	0	5,250
Other Liabilities [Member] | Interest Rate Swap Contracts-Commercial Loans [Member]
Derivatives not Designated as Hedging Instruments
Fair value, Derivatives (included in Other Liabilities)	12,953	13,647
Notional amount, Derivatives (included in Other Liabilities)	245,152	261,754
Collateral Already Posted, Aggregate Fair Value	12,059	12,611
Other Liabilities [Member] | Forward Sale Contracts-Mortgage Loans [Member]
Derivatives not Designated as Hedging Instruments
Fair value, Derivatives (included in Other Liabilities)	57	0
Notional amount, Derivatives (included in Other Liabilities)	$ 7,789	$ 0