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, 2015		Mar. 31, 2014
Derivative Instruments:
Unrealized Gain (Loss)	$ (466,202)		$ (348,942)
Amount of Gain/(Loss) Recognized in Net Gains (Losses) on Trading Assets	(6,896)		(151,824)
Future
Derivative Instruments:
Realized Gain (Loss)	(5,506)		(5,669)
Unrealized Gain (Loss)	(58,126)		(3,048)
Amount of Gain/(Loss) Recognized in Net Gains (Losses) on Trading Assets	(63,632)		(8,717)
TBA Derivatives
Derivative Instruments:
Realized Gain (Loss)	(55,644)	[1]	(37,837)	[1]
Unrealized Gain (Loss)	117,188	[1]	(11,410)	[1]
Amount of Gain/(Loss) Recognized in Net Gains (Losses) on Trading Assets	61,544	[1]	(49,247)	[1]
Interest Rate Swaption
Derivative Instruments:
Realized Gain (Loss)	(21,891)		(40,943)
Unrealized Gain (Loss)	17,083		(52,917)
Amount of Gain/(Loss) Recognized in Net Gains (Losses) on Trading Assets	$ (4,808)		$ (93,860)

[1] Includes options on TBA securities.