Commitments and Contingencies - Estimated Amounts of Regular, Discharge Payments Expected to Pay and Estimated Recoveries from Charged-off Loans (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2015 USD ($)
Summary Of Projections Of Estimated Payments And Recoveries [Line Items]
Estimated Regular Payments	$ 43,720
Estimated Discharge Payments	81,504
Estimated Total Payments	125,224
Estimated Recoveries	(5,985)
2014 [Member]
Summary Of Projections Of Estimated Payments And Recoveries [Line Items]
Estimated Regular Payments	3,713
Estimated Discharge Payments	9,253
Estimated Total Payments	12,966
Estimated Recoveries	(1,396)
2015 [Member]
Summary Of Projections Of Estimated Payments And Recoveries [Line Items]
Estimated Regular Payments	22,392
Estimated Discharge Payments	0
Estimated Total Payments	22,392
Estimated Recoveries	(1,474)
2016 [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	(1,540)
2017 [Member]
Summary Of Projections Of Estimated Payments And Recoveries [Line Items]
Estimated Regular Payments	0
Estimated Discharge Payments	72,251
Estimated Total Payments	72,251
Estimated Recoveries	$ (1,575)