Commitments and Contingencies - Estimated Amounts of Regular, Discharge Payments Expect to Pay and Estimated Recoveries from Charged-off Loans (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014
Summary Of Projections Of Estimated Payments And Recoveries [Line Items]
Estimated Regular Payments	$ 45,233
Estimated Discharge Payments	81,456
Estimated Total Payments	126,689
Estimated Recoveries	(5,997)
2015 [Member]
Summary Of Projections Of Estimated Payments And Recoveries [Line Items]
Estimated Regular Payments	11,723
Estimated Discharge Payments	2,709
Estimated Total Payments	14,432
Estimated Recoveries	(1,393)
2016 [Member]
Summary Of Projections Of Estimated Payments And Recoveries [Line Items]
Estimated Regular Payments	15,895
Estimated Discharge Payments	0
Estimated Total Payments	15,895
Estimated Recoveries	(1,479)
2017 [Member]
Summary Of Projections Of Estimated Payments And Recoveries [Line Items]
Estimated Regular Payments	17,615
Estimated Discharge Payments	0
Estimated Total Payments	17,615
Estimated Recoveries	(1,545)
2018 and Later [Member]
Summary Of Projections Of Estimated Payments And Recoveries [Line Items]
Estimated Regular Payments	0
Estimated Discharge Payments	78,747
Estimated Total Payments	78,747
Estimated Recoveries	$ (1,580)