Estimated Fair Values for All Financial Assets and Liabilities (Detail) - USD ($) $ in Thousands		Mar. 31, 2016		Dec. 31, 2015		Jan. 31, 2014
Financial 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
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
Financial liabilities:
Other secured financing		3,588,326		1,845,048	[1]
Securitized debt of consolidated VIE		3,802,682	[3]	2,540,711	[1],[3]	$ 260,700
Interest rate swaps		2,782,961		1,677,571	[1]
Other derivatives		69,171		49,963
Level 1
Financial assets:
Other derivatives		717		12,443
Financial liabilities:
Other derivatives		69,171		32,778
Level 2
Financial 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
Financial liabilities:
Interest rate swaps		2,782,961		1,677,571
Other derivatives				17,185
Estimate of Fair Value, Fair Value Disclosure | Level 1
Financial assets:
Cash and cash equivalents		2,416,136		1,769,258
Estimate of Fair Value, Fair Value Disclosure | Level 2
Financial 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		906,722
Commercial real estate debt investments		4,401,725		2,911,828
Corporate debt	[4]	626,486		470,894
Interest rate swaps		93,312		19,642
Financial liabilities:
Other secured financing		3,590,225		1,846,095
Securitized debt of consolidated VIE		3,802,898		2,541,193
Participation sold		12,691		13,138
Interest rate swaps		2,782,961		1,677,571
Estimate of Fair Value, Fair Value Disclosure | Level 3
Financial assets:
Commercial real estate debt and preferred equity, held for investment		1,170,280		1,350,968
Loans held for sale		278,600		278,600
Financial liabilities:
Mortgage payable		350,599		339,849
Estimate of Fair Value, Fair Value Disclosure | Level 1, Level 2
Financial assets:
Other derivatives		77,449		22,066
Financial liabilities:
Repurchase agreements		54,562,824		56,361,623
Other derivatives		69,171		49,963
Carrying (Reported) Amount, Fair Value Disclosure | Level 1
Financial assets:
Cash and cash equivalents		2,416,136		1,769,258
Carrying (Reported) Amount, Fair Value Disclosure | Level 2
Financial 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		906,722
Commercial real estate debt investments		4,401,725		2,911,828
Corporate debt	[4]	639,481		488,508
Interest rate swaps		93,312		19,642
Financial liabilities:
Other secured financing		3,588,326		1,845,048
Securitized debt of consolidated VIE		3,802,682		2,540,711
Participation sold		13,182		13,286
Interest rate swaps		2,782,961		1,677,571
Carrying (Reported) Amount, Fair Value Disclosure | Level 3
Financial assets:
Commercial real estate debt and preferred equity, held for investment		1,177,468		1,348,817
Loans held for sale		278,600		278,600
Financial liabilities:
Mortgage payable		334,765		334,707
Carrying (Reported) Amount, Fair Value Disclosure | Level 1, Level 2
Financial assets:
Other derivatives		77,449		22,066
Financial liabilities:
Repurchase agreements		54,448,141		56,230,860
Other derivatives		$ 69,171		$ 49,963

[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.

[3] Includes securitized debt of consolidated VIEs carried at fair value of $3.7 billion and $2.4 billion at March 31, 2016 and December 31, 2015, respectively.

[4] Includes a held-to-maturity debt security carried at amortized cost of $74.7 million as of March 31, 2016 and December 31, 2015. The held-to-maturity debt security had a fair value of $66.8 million and $61.3 million as of March 31, 2016 and December 31, 2015, respectively.