Fair Value Hierarchy for Financial Instruments Not Fair Valued but For Which Fair Value Is Required To Be Disclosed (Detail) - USD ($) $ in Thousands	Jun. 30, 2016		Apr. 30, 2016	Dec. 31, 2015
Fair Value Measurement Inputs Disclosure [Line Items]
Total investment in mortgages and loans, net	$ 1,477,106			$ 1,606,486
Indebtedness	3,005,259		$ 17,696	3,328,082
Junior subordinated notes	10,789			10,504
Level in Fair Value Hierarchy, Three
Fair Value Measurement Inputs Disclosure [Line Items]
Junior subordinated notes	10,789	[1]		10,504	[2]
Carrying Amount
Fair Value Measurement Inputs Disclosure [Line Items]
Total investment in mortgages and loans, net	1,477,106			1,606,486
Indebtedness				63,045
Estimated Fair Value
Fair Value Measurement Inputs Disclosure [Line Items]
Total investment in mortgages and loans,net	1,437,291			1,537,086
Estimated Fair Value | Level in Fair Value Hierarchy, Three
Fair Value Measurement Inputs Disclosure [Line Items]
Total investment in mortgages and loans,net	1,437,291			1,537,086
CMBS securitizations
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness	772,557			885,055
CMBS securitizations | Carrying Amount
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness	586,977			708,510
CMBS securitizations | Estimated Fair Value | Level in Fair Value Hierarchy, Three
Fair Value Measurement Inputs Disclosure [Line Items]
Notes payable, Estimated Fair Value	585,918			709,001
7.0% convertible senior notes | Carrying Amount
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness	843			28,868
7.0% convertible senior notes | Estimated Fair Value | Level in Fair Value Hierarchy, One
Fair Value Measurement Inputs Disclosure [Line Items]
Convertible senior notes, Estimated Fair Value	935			27,795
4.0% convertible senior notes | Carrying Amount
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness	119,474			133,039
4.0% convertible senior notes | Estimated Fair Value | Level in Fair Value Hierarchy, One
Fair Value Measurement Inputs Disclosure [Line Items]
Convertible senior notes, Estimated Fair Value	116,452			104,184
7.625% senior notes due 2024 | Carrying Amount
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness	55,450			57,952
7.625% senior notes due 2024 | Estimated Fair Value | Level in Fair Value Hierarchy, One
Fair Value Measurement Inputs Disclosure [Line Items]
Senior notes, Estimated Fair Value	50,435			46,560
7.125% Senior Notes due 2019 | Carrying Amount
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness	68,899			69,749
7.125% Senior Notes due 2019 | Estimated Fair Value | Level in Fair Value Hierarchy, One
Fair Value Measurement Inputs Disclosure [Line Items]
Senior notes, Estimated Fair Value	69,486			62,471
Senior Secured Notes | Carrying Amount
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness	60,645			63,045
Senior Secured Notes | Estimated Fair Value | Level in Fair Value Hierarchy, Three
Fair Value Measurement Inputs Disclosure [Line Items]
Senior notes, Estimated Fair Value	66,851			66,725
Junior subordinated notes, at amortized cost | Carrying Amount
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness	24,890			24,884
Junior subordinated notes, at amortized cost | Estimated Fair Value | Level in Fair Value Hierarchy, Three
Fair Value Measurement Inputs Disclosure [Line Items]
Junior subordinated notes	11,318			11,221
CDO notes payable, at amortized cost | Carrying Amount
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness	765,299			937,569
CDO notes payable, at amortized cost | Estimated Fair Value | Level in Fair Value Hierarchy, Three
Fair Value Measurement Inputs Disclosure [Line Items]
Notes payable, Estimated Fair Value	633,692			801,289
Loans payable on real estate | Carrying Amount
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness	865,691			811,666
Loans payable on real estate | Estimated Fair Value | Level in Fair Value Hierarchy, Three
Fair Value Measurement Inputs Disclosure [Line Items]
Loans payable on real estate, Estimated Fair Value	$ 910,275			$ 834,816

[1] During the six months ended June 30, 2016, there were no transfers between Level 1 and Level 2, and there were no transfers into and/or out of Level 3.

[2] During the year ended December 31, 2015, there were no transfers between Level 1 and Level 2, and there were no transfers into and/or out of Level 3.