Effect of Other Derivative Contracts on the Consolidated Statements of Operations and Comprehensive Income (Loss) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013
Derivative Instruments:
Unrealized Gain (Loss)	$ (348,942)		$ 325,734
Net Gains (Losses) on Trading Assets	(151,824)		7,709
Other Derivative Contracts | TBA Derivatives
Derivative Instruments:
Realized Gain (Loss)	(37,837)	[1]	9,340
Unrealized Gain (Loss)	(11,410)	[1]	(1,875)
Net Gains (Losses) on Trading Assets	(49,247)	[1]	7,465
Other Derivative Contracts | Interest Rate Swaption
Derivative Instruments:
Realized Gain (Loss)	(40,943)
Unrealized Gain (Loss)	(52,917)
Net Gains (Losses) on Trading Assets	(93,860)
Other Derivative Contracts | Us Treasury futures
Derivative Instruments:
Realized Gain (Loss)	(5,669)		12,702
Unrealized Gain (Loss)	(3,048)		(12,458)
Net Gains (Losses) on Trading Assets	$ (8,717)		$ 244

[1] Includes options on TBA securities.