Derivative Instruments and Hedging Activities - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Derivative [Line Items]
Notional amount of interest rate derivatives	$ 22,800,000		$ 22,800,000
Maturity date, derivative instrument			Jul. 15, 2015
Change in fair value of swap	(4,818,000)	(2,101,000)	(1,443,000)	(5,840,000)
Aggregate fair value of net liability position	13,900,000		13,900,000
Collateral posted with counterparties	31,700,000		31,700,000
Interest Rate Swaps [Member]
Derivative [Line Items]
Accumulated net after-tax losses related to effective cash flow hedges	9,900,000		9,900,000		12,700,000
Estimated amount of interest rate derivatives to be reclassified to interest expense			8,400,000
Recognized a net reduction to interest expense	183,000	141,000	470,000	416,000
Interest Rate Swaps [Member] | Cash Flow Hedge [Member]
Derivative [Line Items]
Notional amount of interest rate derivatives	300,000,000		300,000,000
Forward-Settle Interest Rate Swap [Member] | Cash Flow Hedge [Member]
Derivative [Line Items]
Notional amount of interest rate derivatives	65,000,000		65,000,000
Change in fair value of swap			1,000,000
Derivative [Member]
Derivative [Line Items]
Gain (loss) on cash flow hedge ineffectiveness				73,000
Customer Repurchase Agreements and Money Market Deposit Accounts [Member] | Interest Rate Swaps Due July Twelve Two Thousand Twelve [Member] | Cash Flow Hedge [Member]
Derivative [Line Items]
Notional amount of interest rate derivatives	100,000,000		100,000,000
Customer Repurchase Agreements and Money Market Deposit Accounts [Member] | Interest Rate Swaps Due July Fifteen Two Thousand Fifteen [Member]
Derivative [Line Items]
Aggregate notional amount of interest rate derivatives	100,000,000		100,000,000
Derivatives Designated as Hedging Instruments [Member] | Interest Rate Swaps [Member]
Derivative [Line Items]
Aggregate notional amount of interest rate derivatives	300,000,000		300,000,000
Derivatives Designated as Hedging Instruments [Member] | Interest Rate Swaps [Member] | Minimum [Member]
Derivative [Line Items]
Maturity date, derivative instrument			Nov. 01, 2018
Fixed interest rate	2.57%		2.57%
Derivatives Designated as Hedging Instruments [Member] | Interest Rate Swaps [Member] | Maximum [Member]
Derivative [Line Items]
Maturity date, derivative instrument			Nov. 01, 2020
Fixed interest rate	2.97%		2.97%
Interest rate swap, starting date	November 2015		November 2015
Derivatives Designated as Hedging Instruments [Member] | Consumer and Commercial Money Market Deposit Accounts [Member]
Derivative [Line Items]
Maturity date, derivative instrument			Sep. 27, 2023
Strike rates	7.44%		7.44%
Derivatives Designated as Hedging Instruments [Member] | Consumer and Commercial Money Market Deposit Accounts [Member] | Minimum [Member]
Derivative [Line Items]
Strike rates	6.00%		6.00%
Derivatives Designated as Hedging Instruments [Member] | Consumer and Commercial Money Market Deposit Accounts [Member] | Maximum [Member]
Derivative [Line Items]
Strike rates	6.25%		6.25%
Derivatives Designated as Hedging Instruments [Member] | Consumer and Commercial Money Market Deposit Accounts [Member] | Interest Rate Swaps [Member] | Fair Value Hedge [Member]
Derivative [Line Items]
Notional amount of interest rate derivatives	8,600,000		8,600,000
Derivatives Designated as Hedging Instruments [Member] | Consumer and Commercial Money Market Deposit Accounts [Member] | Interest Rate Swaps [Member] | Fixed-Rate at Approximately 4.73% [Member]
Derivative [Line Items]
Aggregate notional amount of interest rate derivatives	200,000,000		200,000,000
Maturity date, derivative instrument			Oct. 01, 2016
Fixed interest rate	4.73%		4.73%
Interest rate swap, starting date	July 2012		July 2012
Derivatives Designated as Hedging Instruments [Member] | Consumer and Commercial Money Market Deposit Accounts [Member] | Interest Rate Swaps [Member] | Fixed-Rate at Approximately 5.11% [Member]
Derivative [Line Items]
Maturity date, derivative instrument			Jul. 01, 2017
Fixed interest rate	5.11%		5.11%
Derivatives Designated as Hedging Instruments [Member] | Consumer and Commercial Money Market Deposit Accounts [Member] | Interest Rate Swaps Due September Twenty Seven Two Thousand Twenty Three [Member]
Derivative [Line Items]
Aggregate notional amount of interest rate derivatives	125,000,000		125,000,000
Derivatives Designated as Hedging Instruments [Member] | Customer Repurchase Agreements and Money Market Deposit Accounts [Member] | Interest Rate Swaps [Member] | Fixed-Rate at Approximately 4.73% [Member]
Derivative [Line Items]
Maturity date, derivative instrument			Mar. 01, 2014
Derivatives Designated as Hedging Instruments [Member] | Customer Repurchase Agreements and Money Market Deposit Accounts [Member] | Interest Rate Swaps [Member] | Fixed-Rate at Approximately 4.73% [Member] | Fair Value Hedge [Member]
Derivative [Line Items]
Notional amount of interest rate derivatives	51,000,000		51,000,000
Derivatives Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Total interest rate swaps aggregate notional amount	$ 255,400,000		$ 255,400,000
Number of interest rate swaps	49		49