Estimated Fair Values for All Financial Assets and Liabilities (Detail) - USD ($) $ in Thousands		Jun. 30, 2016		Dec. 31, 2015		Jan. 31, 2014
Financial assets:
Agency mortgage-backed securities		$ 64,862,992		$ 65,718,224
Agency debentures	[1]			152,038
Credit risk transfer securities		520,321		456,510	[1]
Non-Agency mortgage-backed securities		1,197,549
Commercial real estate debt investments	[2]	4,361,972		2,911,828	[1]
Loans held for sale, net		164,175		278,600	[1]
Interest rate swaps		146,285		19,642	[1]
Other derivatives		137,490		22,066
Financial liabilities:
Other secured financing		3,588,326		1,845,048	[1]
Securitized debt of consolidated VIE		3,748,289	[3]	2,540,711	[1],[3]	$ 260,700
Interest rate swaps		3,208,986		1,677,571	[1]
Other derivatives		154,017		49,963
Level 1
Financial assets:
Other derivatives				12,443
Financial liabilities:
Other derivatives		154,017		32,778
Level 2
Financial assets:
Agency mortgage-backed securities		64,862,992		65,718,224
Agency debentures				152,038
Credit risk transfer securities		520,321		456,510
Non-Agency mortgage-backed securities		1,197,549
Commercial real estate debt investments		4,361,972		2,911,828
Interest rate swaps		146,285		19,642
Other derivatives		137,490		9,623
Financial liabilities:
Interest rate swaps		3,208,986		1,677,571
Other derivatives				17,185
Estimate of Fair Value, Fair Value Disclosure | Level 1
Financial assets:
Cash and cash equivalents		2,735,250		1,769,258
Estimate of Fair Value, Fair Value Disclosure | Level 2
Financial assets:
Agency mortgage-backed securities		64,862,992		65,718,224
Agency debentures				152,038
Credit risk transfer securities		520,321		456,510
Non-Agency mortgage-backed securities		1,197,549		906,722
Commercial real estate debt investments		4,361,972		2,911,828
Corporate debt	[4]	661,169		470,894
Interest rate swaps		146,285		19,642
Financial liabilities:
Securitized debt of consolidated VIE		3,748,366		2,541,193
Participation sold		12,985		13,138
Interest rate swaps		3,208,986		1,677,571
Estimate of Fair Value, Fair Value Disclosure | Level 3
Financial assets:
Commercial real estate debt and preferred equity, held for investment		1,137,130		1,350,968
Loans held for sale, net		165,000		278,600
Financial liabilities:
Mortgage payable		350,065		339,849
Estimate of Fair Value, Fair Value Disclosure | Level 1, Level 2
Financial assets:
Other derivatives		137,490		22,066
Financial liabilities:
Repurchase agreements		53,976,010		56,361,623
Other secured financing		3,590,510		1,846,095
Other derivatives		154,017		49,963
Carrying (Reported) Amount, Fair Value Disclosure | Level 1
Financial assets:
Cash and cash equivalents		2,735,250		1,769,258
Carrying (Reported) Amount, Fair Value Disclosure | Level 2
Financial assets:
Agency mortgage-backed securities		64,862,992		65,718,224
Agency debentures				152,038
Credit risk transfer securities		520,321		456,510
Non-Agency mortgage-backed securities		1,197,549		906,722
Commercial real estate debt investments		4,361,972		2,911,828
Corporate debt	[4]	669,612		488,508
Interest rate swaps		146,285		19,642
Financial liabilities:
Securitized debt of consolidated VIE		3,748,289		2,540,711
Participation sold		13,079		13,286
Interest rate swaps		3,208,986		1,677,571
Carrying (Reported) Amount, Fair Value Disclosure | Level 3
Financial assets:
Commercial real estate debt and preferred equity, held for investment		1,137,971		1,348,817
Loans held for sale, net		164,175		278,600
Financial liabilities:
Mortgage payable		327,643		334,707
Carrying (Reported) Amount, Fair Value Disclosure | Level 1, Level 2
Financial assets:
Other derivatives		137,490		22,066
Financial liabilities:
Repurchase agreements		53,868,385		56,230,860
Other secured financing		3,588,326		1,845,048
Other derivatives		$ 154,017		$ 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 June 30, 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 June 30, 2016 and December 31, 2015, respectively.

[4] Includes a held-to-maturity debt security carried at amortized cost of $84.4 million and $74.7 million as of June 30, 2016 and December 31, 2015, respectively. The held-to-maturity debt security had a fair value of $80.8 million and $61.3 million as of June 30, 2016 and December 31, 2015, respectively.