Fair Value Measurements (Detail) - USD ($) $ in Thousands		Sep. 30, 2016	Dec. 31, 2015
Assets:
Agency mortgage-backed securities		$ 73,476,105	$ 65,718,224
Non-Agency mortgage-backed securities		75,605,661	67,233,494
Agency debentures	[1]		152,038
Credit risk transfer securities		669,295	456,510	[1]
Non-Agency mortgage-backed securities		1,460,261
Mortgage servicing rights		492,169
Commercial real estate debt investments	[2]	4,319,077	2,911,828	[1]
Interest rate swaps		113,253	19,642	[1]
Other derivatives		87,921	22,066
Total assets		80,928,229	70,187,030
Liabilities:
Securitized debt of consolidated VIEs		3,712,821	2,366,878	[1]
Interest rate swaps		2,919,492	1,677,571	[1]
Other derivatives		73,445	49,963
Total liabilities		6,705,758	4,094,412
Non-Agency mortgage-backed securities
Assets:
Non-Agency mortgage-backed securities	[3]	1,460,261	906,722	[1]
Residential Mortgage
Assets:
Residential mortgage loans		310,148
Level 1
Assets:
Other derivatives		26,985	12,443
Total assets		26,985	12,443
Liabilities:
Other derivatives		70,784	32,778
Total liabilities		70,784	32,778
Level 2
Assets:
Agency mortgage-backed securities		73,476,105	65,718,224
Agency debentures			152,038
Credit risk transfer securities		669,295	456,510
Non-Agency mortgage-backed securities		1,460,261
Commercial real estate debt investments		4,319,077	2,911,828
Interest rate swaps		113,253	19,642
Other derivatives		60,936	9,623
Total assets		80,409,075	70,174,587
Liabilities:
Securitized debt of consolidated VIEs		3,712,821	2,366,878
Interest rate swaps		2,919,492	1,677,571
Other derivatives		2,661	17,185
Total liabilities		6,634,974	4,061,634
Level 2 | Non-Agency mortgage-backed securities
Assets:
Non-Agency mortgage-backed securities			$ 906,722
Level 2 | Residential Mortgage
Assets:
Residential mortgage loans		310,148
Level 3
Assets:
Mortgage servicing rights		492,169
Total assets		$ 492,169

[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 September 30, 2016 and December 31, 2015, respectively.

[3] Includes $96.0 million and $0 at September 30, 2016 and December 31, 2015, respectively, of non-Agency mortgage-backed securities pledged as collateral in a consolidated VIE and eliminated from the Company's Consolidated Statements of Financial Condition.