Estimated Fair Values for All Financial Assets and Liabilities (Detail) - USD ($) $ in Thousands		Dec. 31, 2016	Dec. 31, 2015
Estimate of Fair Value, Fair Value Disclosure
Financial assets:
Commercial loans held for sale, net		$ 114,425	$ 278,600
Estimate of Fair Value, Fair Value Disclosure | Level 1
Financial assets:
Cash and cash equivalents		1,539,746	1,769,258
Estimate of Fair Value, Fair Value Disclosure | Level 2
Financial assets:
Agency mortgage-backed securities		75,589,873	65,718,224
Agency debentures			152,038
Credit risk transfer securities		724,722	456,510
Non-Agency mortgage-backed securities		1,401,307	906,722
Commercial real estate debt investments		4,321,739	2,911,828
Corporate debt		776,310	470,894
Interest rate swaps		68,194	19,642
Residential mortgage loans		342,289
Financial liabilities:
Securitized debt of consolidated VIEs		3,655,802	2,541,193
Participation sold		12,827	13,138
Interest rate swaps		1,443,765	1,677,571
Estimate of Fair Value, Fair Value Disclosure | Level 3
Financial assets:
Mortgage servicing rights		652,216
Commercial real estate debt and preferred equity, held for investment		968,824	1,350,968
Financial liabilities:
Mortgage payable		312,442	339,849
Estimate of Fair Value, Fair Value Disclosure | Level 1, Level 2
Financial assets:
Other derivatives		171,266	22,066
Financial liabilities:
Repurchase agreements		65,256,505	56,361,623
Other secured financing		3,885,430	1,846,095
Other derivatives		86,437	49,963
Carrying (Reported) Amount, Fair Value Disclosure
Financial assets:
Commercial loans held for sale, net		114,425	278,600
Carrying (Reported) Amount, Fair Value Disclosure | Level 1
Financial assets:
Cash and cash equivalents		1,539,746	1,769,258
Carrying (Reported) Amount, Fair Value Disclosure | Level 2
Financial assets:
Agency mortgage-backed securities		75,589,873	65,718,224
Agency debentures			152,038
Credit risk transfer securities		724,722	456,510
Non-Agency mortgage-backed securities		1,401,307	906,722
Residential mortgage loans		342,289
Commercial real estate debt investments		4,321,739	2,911,828
Corporate debt		773,274	488,508
Interest rate swaps	[1]	68,194	19,642
Financial liabilities:
Securitized debt of consolidated VIEs		3,655,802	2,540,711
Participation sold		12,869	13,286
Interest rate swaps		1,443,765	1,677,571
Carrying (Reported) Amount, Fair Value Disclosure | Level 3
Financial assets:
Mortgage servicing rights		652,216
Commercial real estate debt and preferred equity, held for investment		970,505	1,348,817
Financial liabilities:
Mortgage payable		311,636	334,707
Carrying (Reported) Amount, Fair Value Disclosure | Level 1, Level 2
Financial assets:
Other derivatives		171,266	22,066
Financial liabilities:
Repurchase agreements		65,215,810	56,230,860
Other secured financing		3,884,708	1,845,048
Other derivatives		86,437	49,963
Agency mortgage-backed securities		75,589,873	65,718,224
Agency debentures			152,038
Credit risk transfer securities		724,722	456,510
Non-Agency mortgage-backed securities		1,401,307
Residential mortgage loans	[2]	342,289
Mortgage servicing rights		652,216
Commercial real estate debt investments	[3]	4,321,739	2,911,828
Interest rate swaps		68,194	19,642
Other derivatives		171,266	22,066
Other secured financing		3,884,708	1,845,048
Securitized debt of consolidated VIEs	[4]	3,655,802	2,540,711
Interest rate swaps		1,443,765	1,677,571
Other derivatives		86,437	49,963
Level 1
Financial assets:
Other derivatives		168,209	12,443
Financial liabilities:
Other derivatives		24,912	32,778
Level 2
Financial assets:
Agency mortgage-backed securities		75,589,873	65,718,224
Agency debentures			152,038
Credit risk transfer securities		724,722	456,510
Non-Agency mortgage-backed securities		1,401,307
Commercial real estate debt investments		4,321,739	2,911,828
Interest rate swaps		68,194	19,642
Other derivatives		3,057	9,623
Financial liabilities:
Interest rate swaps		1,443,765	1,677,571
Other derivatives		$ 61,525	$ 17,185

[1] Includes a held-to-maturity debt security carried at amortized cost of $84.5 million, with a fair value of $87.8 million, and $74.7 million, with a fair value of $61.3 million, as of December 31, 2016 and 2015, respectively. The bond's stated maturity is May 15, 2020.

[2] Includes securitized residential mortgage loans of a consolidated VIE carried at fair value of $165.9 million and $0 at December 31, 2016 and 2015, respectively.

[3] Includes senior securitized commercial mortgage loans of consolidated VIEs carried at fair value of $3.9 billion and $2.6 billion at December 31, 2016 and 2015, respectively.

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