Derivative Financial Instruments Schedule of the changes in the fair value of non-hedge accounting derivatives (Detail) (Not Designated as Hedging Instrument [Member], Interest Expense [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Derivative [Line Items]
Net increase to other non-interest income	$ 1,470	$ 1,061	$ 4,750	$ 2,854
Non-hedge derivatives, net [Member]
Derivative [Line Items]
Net increase to other non-interest income	1,769	1,511	5,335	3,144
Fed funds futures contracts [Member]
Derivative [Line Items]
Net increase to other non-interest income	$ (299)	$ (450)	$ (585)	$ (290)