Fair Value Hierarchy for Financial Instruments Not Fair Valued but For Which Fair Value Is Required To Be Disclosed (Detail) - USD ($) $ in Thousands	Sep. 30, 2016		Apr. 30, 2016	Dec. 31, 2015
Fair Value Measurement Inputs Disclosure [Line Items]
Total investment in mortgages and loans, net	$ 1,354,960			$ 1,606,486
Indebtedness	1,975,863		$ 17,696	2,399,475
Junior subordinated notes	11,524			10,504
Significant Unobservable Inputs (Level 3)
Fair Value Measurement Inputs Disclosure [Line Items]
Junior subordinated notes	11,524	[1]		10,504	[2]
Carrying Amount
Fair Value Measurement Inputs Disclosure [Line Items]
Total investment in mortgages and loans, net	1,354,960			1,606,486
Indebtedness				63,045
Estimated Fair Value
Fair Value Measurement Inputs Disclosure [Line Items]
Total investment in mortgages and loans,net	1,321,940			1,537,086
Estimated Fair Value | Significant Unobservable Inputs (Level 3)
Fair Value Measurement Inputs Disclosure [Line Items]
Total investment in mortgages and loans,net	1,321,940			1,537,086
CMBS securitizations | Carrying Amount
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness	492,493			708,510
CMBS securitizations | Estimated Fair Value | Significant Unobservable Inputs (Level 3)
Fair Value Measurement Inputs Disclosure [Line Items]
Notes payable, Estimated Fair Value	494,264			709,001
7.0% convertible senior notes | Carrying Amount
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness	844			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	951			27,795
4.0% convertible senior notes | Carrying Amount
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness	119,883			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	117,271			104,184
7.625% senior notes due 2024 | Carrying Amount
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness	55,540			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	51,329			46,560
7.125% Senior Notes due 2019 | Carrying Amount
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness	69,186			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	69,062			62,471
Senior Secured Notes | Carrying Amount
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness	59,440			63,045
Senior Secured Notes | Estimated Fair Value | Significant Unobservable Inputs (Level 3)
Fair Value Measurement Inputs Disclosure [Line Items]
Senior notes, Estimated Fair Value	64,596			66,725
Junior subordinated notes, at amortized cost | Carrying Amount
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness	24,892			24,884
Junior subordinated notes, at amortized cost | Estimated Fair Value | Significant Unobservable Inputs (Level 3)
Fair Value Measurement Inputs Disclosure [Line Items]
Junior subordinated notes	12,262			11,221
CDO notes payable, at amortized cost | Carrying Amount
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness	719,197			937,569
CDO notes payable, at amortized cost | Estimated Fair Value | Significant Unobservable Inputs (Level 3)
Fair Value Measurement Inputs Disclosure [Line Items]
Notes payable, Estimated Fair Value	639,060			801,289
Loans payable on real estate | Carrying Amount
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness	229,820			268,632
Loans payable on real estate | Estimated Fair Value | Significant Unobservable Inputs (Level 3)
Fair Value Measurement Inputs Disclosure [Line Items]
Loans payable on real estate, Estimated Fair Value	$ 238,856			$ 281,840

[1] During the nine months ended September 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.