Commitments and Contingencies - Gains (Losses) Related to Derivative Instruments not Designated as Hedging Instruments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Other non-interest income	$ 15,979	$ 18,636	$ 18,626	$ 20,574	$ 21,720	$ 18,564	$ 18,091	$ 39,551	$ 21,969	$ 15,921	$ 16,015
Derivatives not designated as hedging instrument [Member]
Trading gains, net											1,984
Other non-interest income									$ 253		$ 369