Derivative Instruments and Other Hedging Activities - Schedule of Derivative Instruments on Consolidated Financial Statements (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Derivative Instruments And Hedging Activities [Line Items]
Amount of Gain (Loss) Recognized in OCI, net of taxes (Effective Portion)	$ 751	$ 1,558
Amount of Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	(424)	(386)
Amount of Gain (Loss) Recognized in Income on Derivative (Ineffective Portion and Amount Excluded from Effectiveness Testing)
Amount of Gain (Loss) Recognized in Income on Derivatives	(1)
Not Designated As Hedging Instruments [Member]
Derivative Instruments And Hedging Activities [Line Items]
Amount of Gain (Loss) Recognized in Income on Derivatives	(1,828)	56
Other Income (Expense) [Member] | Interest Rate Contracts [Member] | Not Designated As Hedging Instruments [Member]
Derivative Instruments And Hedging Activities [Line Items]
Amount of Gain (Loss) Recognized in Income on Derivatives	(1)
Mortgage income [Member] | Forward Sale Contracts [Member] | Not Designated As Hedging Instruments [Member]
Derivative Instruments And Hedging Activities [Line Items]
Amount of Gain (Loss) Recognized in Income on Derivatives	(2,912)
Mortgage income [Member] | Written And Purchased Options [Member] | Not Designated As Hedging Instruments [Member]
Derivative Instruments And Hedging Activities [Line Items]
Amount of Gain (Loss) Recognized in Income on Derivatives	1,085	56
Cash Flow Hedging [Member] | Interest Rate Contracts [Member]
Derivative Instruments And Hedging Activities [Line Items]
Amount of Gain (Loss) Recognized in OCI, net of taxes (Effective Portion)	751	1,558
Amount of Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	(424)	(386)
Amount of Gain (Loss) Recognized in Income on Derivative (Ineffective Portion and Amount Excluded from Effectiveness Testing)