Contingencies - Estimated Amounts of Regular, Discharge Payments Expected to Pay and Estimated Recoveries from Charged-off Loans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013
Summary Of Projections Of Estimated Payments And Recoveries [Line Items]
Estimated Regular Payments	$ 0
Estimated Discharge Payments	42,096
Estimated Total Payments	42,096
Estimated Recoveries	(9,784)
2013 [Member]
Summary Of Projections Of Estimated Payments And Recoveries [Line Items]
Estimated Regular Payments	0
Estimated Discharge Payments	26,795
Estimated Total Payments	26,795
Estimated Recoveries	(650)
2014 [Member]
Summary Of Projections Of Estimated Payments And Recoveries [Line Items]
Estimated Regular Payments	0
Estimated Discharge Payments	11,050
Estimated Total Payments	11,050
Estimated Recoveries	(1,820)
2015 [Member]
Summary Of Projections Of Estimated Payments And Recoveries [Line Items]
Estimated Regular Payments	0
Estimated Discharge Payments	3,576
Estimated Total Payments	3,576
Estimated Recoveries	(2,440)
2016 [Member]
Summary Of Projections Of Estimated Payments And Recoveries [Line Items]
Estimated Regular Payments	0
Estimated Discharge Payments	613
Estimated Total Payments	613
Estimated Recoveries	(2,440)
2017 and Later [Member]
Summary Of Projections Of Estimated Payments And Recoveries [Line Items]
Estimated Regular Payments	0
Estimated Discharge Payments	62
Estimated Total Payments	62
Estimated Recoveries	$ (2,434)