Derivative Instruments and Hedging Activities - Gains Related to Derivative Instruments Not Designated as Hedging Instruments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Non-designated hedge interest rate derivatives
Other non-interest income	$ 1,461	$ 1	$ 1,090	$ 217