Summary of Fair Value Information about Derivative Assets and Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Derivatives, Fair Value [Line Items]
Interest rate swaps, at fair value	$ 93,312	$ 19,642	[1]
Other derivatives, at fair value	77,449	22,066	[1]
Derivative assets	170,761	41,708
Interest rate swaps, at fair value	2,782,961	1,677,571	[1]
Other derivatives, at fair value	69,171	49,963	[1]
Derivative liabilities	2,852,132	1,727,534
Future
Derivatives, Fair Value [Line Items]
Other derivatives, at fair value	717	12,444
Other derivatives, at fair value	69,171	32,778
TBA Derivatives
Derivatives, Fair Value [Line Items]
Other derivatives, at fair value	$ 76,732	9,622
Other derivatives, at fair value		$ 17,185

[1] Derived from the audited consolidated financial statements at December 31, 2015.