Fair value and the undiscounted amount of the tru-up payment obligation (Detail) (Federal Deposit Insurance Corporation [Member], USD $) In Thousands, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Federal Deposit Insurance Corporation [Member]
Loss Share Indemnification Asset [Line Items]
Business Acquisition, Contingent Consideration, at Fair Value	$ 103,189		$ 98,340
Business Acquisition, Contingent Consideration, Potential Cash Payment	$ 171,654	[1]	$ 170,973	[1]

[1] Increase from December 31, 2011 was due to changes in expected cash flows on the covered assets.