Derivative Instruments and Hedging Activities - Value of Derivative Assets and Derivative Liabilities (Detail) - Not Designated as Hedging Instruments [Member] - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Derivatives not Designated as Hedging Instruments
Fair value, Derivatives (included in Other Assets)	$ 14,232	$ 12,981
Fair value, Derivatives (included in Other Liabilities)	14,184	12,953
Other Assets [Member] | Interest Rate Swaps [Member]
Derivatives not Designated as Hedging Instruments
Fair value, Derivatives (included in Other Assets)	14,232	12,981
Notional amount, Derivatives (included in Other Assets)	239,277	245,152
Other Assets [Member] | Interest Rate Lock Commitments [Member]
Derivatives not Designated as Hedging Instruments
Fair value, Derivatives (included in Other Assets)	574	235
Notional amount, Derivatives (included in Other Assets)	16,969	8,822
Other Assets [Member] | Forward Sale Contracts [Member]
Derivatives not Designated as Hedging Instruments
Fair value, Derivatives (included in Other Assets)	0
Notional amount, Derivatives (included in Other Assets)	0
Other Liabilities [Member] | Interest Rate Swap Contracts-Commercial Loans [Member]
Derivatives not Designated as Hedging Instruments
Collateral posted	12,548	12,059
Other Liabilities [Member] | Interest Rate Swaps [Member]
Derivatives not Designated as Hedging Instruments
Fair value, Derivatives (included in Other Liabilities)	14,184	12,953
Notional amount, Derivatives (included in Other Liabilities)	239,277	245,152
Other Liabilities [Member] | Forward Sale Contracts [Member]
Derivatives not Designated as Hedging Instruments
Fair value, Derivatives (included in Other Liabilities)	126	57
Notional amount, Derivatives (included in Other Liabilities)	$ 14,320	$ 7,789