Effect of Other Derivative Contracts on the Consolidated Statements of Operations and Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Derivative Instruments:
Unrealized Gain (Loss)		$ (373,220)	$ 700,792	$ (1,404,940)	$ 234,590
Amount of Gain/(Loss) Recognized in Net Gains (Losses) on Trading Assets		81,880	(114,221)	207,052	(121,119)
Us Treasury futures
Derivative Instruments:
Realized Gain (Loss)		8,314	(9,230)	(122,680)	(14,737)
Unrealized Gain (Loss)		(85,563)	53,351	(133,683)	(4,775)
Amount of Gain/(Loss) Recognized in Net Gains (Losses) on Trading Assets		(77,249)	44,121	(256,363)	(19,512)
TBA Derivatives
Derivative Instruments:
Realized Gain (Loss)	[1]	98,371	(50,801)	318,363	(106,445)
Unrealized Gain (Loss)	[1]	60,758	(106,974)	145,052	10,213
Amount of Gain/(Loss) Recognized in Net Gains (Losses) on Trading Assets	[1]	$ 159,129	(157,775)	$ 463,415	(96,232)
Interest Rate Swaption
Derivative Instruments:
Realized Gain (Loss)			(7,600)		(29,491)
Unrealized Gain (Loss)			7,033		24,116
Amount of Gain/(Loss) Recognized in Net Gains (Losses) on Trading Assets			$ (567)		$ (5,375)

[1] Includes options on TBA contracts.