Fair Value Measurements (Detail) - USD ($) $ in Thousands		Mar. 31, 2016	Dec. 31, 2015
Assets:
Agency mortgage-backed securities		$ 65,439,824	$ 65,718,224
Agency debentures		157,035	152,038	[1]
Credit risk transfer securities		501,167	456,510	[1]
Non-Agency mortgage-backed securities		1,157,507
Non-Agency mortgage-backed securities		67,255,533	67,233,494
Commercial real estate debt investments	[2]	4,401,725	2,911,828	[1]
Interest rate swaps		93,312	19,642	[1]
Other derivatives		77,449	22,066
Total assets		71,828,019	70,187,030
Liabilities:
Securitized debt of consolidated VIEs		3,677,079	2,366,878	[1]
Interest rate swaps		2,782,961	1,677,571	[1]
Other derivatives		69,171	49,963
Total liabilities		6,529,211	4,094,412
Non-Agency mortgage-backed securities [Member]
Assets:
Non-Agency mortgage-backed securities		1,157,507	906,722	[1]
Level 1
Assets:
Other derivatives		717	12,443
Total assets		717	12,443
Liabilities:
Other derivatives		69,171	32,778
Total liabilities		69,171	32,778
Level 2
Assets:
Agency mortgage-backed securities		65,439,824	65,718,224
Agency debentures		157,035	152,038
Credit risk transfer securities		501,167	456,510
Non-Agency mortgage-backed securities		1,157,507
Commercial real estate debt investments		4,401,725	2,911,828
Interest rate swaps		93,312	19,642
Other derivatives		76,732	9,623
Total assets		71,827,302	70,174,587
Liabilities:
Securitized debt of consolidated VIEs		3,677,079	2,366,878
Interest rate swaps		2,782,961	1,677,571
Other derivatives			17,185
Total liabilities		$ 6,460,040	4,061,634
Level 2 | Non-Agency mortgage-backed securities [Member]
Assets:
Non-Agency mortgage-backed securities			$ 906,722

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

[2] Includes senior securitized commercial mortgage loans of consolidated VIEs carried at fair value of $4.0 billion and $2.6 billion at March 31, 2016 and December 31, 2015, respectively.