Effect of Other Derivative Contracts on the Consolidated Statements of Operations and Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Derivative Instruments:
Unrealized Gain (Loss)		$ 256,462	$ (822,585)	$ (1,148,478)	$ (587,995)
Amount of Gain/(Loss) Recognized in Net Gains (Losses) on Trading Assets		162,981	108,179	370,034	(12,942)
Us Treasury Futures
Derivative Instruments:
Realized Gain (Loss)		(47,035)	(36,468)	(169,716)	(51,205)
Unrealized Gain (Loss)		110,218	(105,199)	(23,465)	(109,974)
Amount of Gain/(Loss) Recognized in Net Gains (Losses) on Trading Assets		63,183	(141,667)	(193,181)	(161,179)
Purchase Commitments
Derivative Instruments:
Unrealized Gain (Loss)		116		116
Amount of Gain/(Loss) Recognized in Net Gains (Losses) on Trading Assets		116		116
TBA Derivatives
Derivative Instruments:
Realized Gain (Loss)	[1]	174,086	168,292	492,450	61,846
Unrealized Gain (Loss)	[1]	(78,677)	81,560	66,376	91,773
Amount of Gain/(Loss) Recognized in Net Gains (Losses) on Trading Assets	[1]	95,409	249,852	558,826	153,619
Interest Rate Swaptions
Derivative Instruments:
Realized Gain (Loss)		4,180	(11,525)	4,180	(41,016)
Unrealized Gain (Loss)		93	11,519	93	35,634
Amount of Gain/(Loss) Recognized in Net Gains (Losses) on Trading Assets		$ 4,273	$ (6)	$ 4,273	$ (5,382)

[1] Includes options on TBA contracts.