Contingencies - Estimated Amounts of Regular, Discharge Payments Expected to Pay and Estimated Recoveries from Charged-off Loans (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013
Summary Of Projections Of Estimated Payments And Recoveries [Line Items]
Estimated Regular Payments	$ 0
Estimated Discharge Payments	42,865
Estimated Total Payments	42,865
Estimated Recoveries	(10,183)
2013 [Member]
Summary Of Projections Of Estimated Payments And Recoveries [Line Items]
Estimated Regular Payments	0
Estimated Discharge Payments	27,027
Estimated Total Payments	27,027
Estimated Recoveries	(650)
2014 [Member]
Summary Of Projections Of Estimated Payments And Recoveries [Line Items]
Estimated Regular Payments	0
Estimated Discharge Payments	10,432
Estimated Total Payments	10,432
Estimated Recoveries	(1,820)
2015 [Member]
Summary Of Projections Of Estimated Payments And Recoveries [Line Items]
Estimated Regular Payments	0
Estimated Discharge Payments	4,333
Estimated Total Payments	4,333
Estimated Recoveries	(2,490)
2016 [Member]
Summary Of Projections Of Estimated Payments And Recoveries [Line Items]
Estimated Regular Payments	0
Estimated Discharge Payments	933
Estimated Total Payments	933
Estimated Recoveries	(2,570)
2017 and Later [Member]
Summary Of Projections Of Estimated Payments And Recoveries [Line Items]
Estimated Regular Payments	0
Estimated Discharge Payments	140
Estimated Total Payments	140
Estimated Recoveries	$ (2,653)