Carrying Amount and Fair Value of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013		Mar. 31, 2013	Dec. 31, 2012
Assets
Commercial mortgages, mezzanine loans, other loans and preferred equity interests, Carrying Amount	$ 1,235,155		$ 1,122,377
Investments in securities and security-related receivables, Carrying Amount	573,739		567,302
Cash and cash equivalents, Carrying Amount	110,072		88,847		63,854	100,041
Restricted cash, Carrying Amount	92,497		121,589
Derivative assets	946		1,305
Liabilities
Junior subordinated notes	12,515		11,911
Carrying Amount	2,257,238		2,086,401
Notes payable, Estimated Fair Value	399,448		377,235
Derivative liabilities	102,796		113,331
Recourse Indebtedness
Liabilities
Carrying Amount	307,176	[1]	235,011	[2]
Non-recourse indebtedness
Liabilities
Carrying Amount	1,950,062		1,851,390
Carrying Amount
Assets
Commercial mortgages, mezzanine loans, other loans and preferred equity interests, Carrying Amount	1,220,876		1,122,377
Investments in securities and security-related receivables, Carrying Amount	573,739		567,302
Cash and cash equivalents, Carrying Amount	110,072		88,847
Restricted cash, Carrying Amount	92,497		121,589
Carrying Amount | Derivative assets
Assets
Derivative assets	946		1,305
Carrying Amount | 7.0% convertible senior notes
Liabilities
Carrying Amount	33,058		32,938
Carrying Amount | 4.0% Convertible Senior Notes
Liabilities
Carrying Amount	132,419		116,184
Carrying Amount | Junior subordinated notes, at amortized cost
Liabilities
Carrying Amount	25,100		25,100
Carrying Amount | CDO notes payable, at amortized cost
Liabilities
Carrying Amount	1,161,735		1,202,772
Carrying Amount | CMBS securitization
Liabilities
Carrying Amount	89,331		100,139
Carrying Amount | Loans payable on real estate
Liabilities
Carrying Amount	299,548		171,244
Carrying Amount | Recourse Indebtedness | 7.0% convertible senior notes
Liabilities
Carrying Amount	33,058		32,938
Carrying Amount | Recourse Indebtedness | 4.0% Convertible Senior Notes
Liabilities
Carrying Amount	132,419		116,184
Carrying Amount | Recourse Indebtedness | Secured credit facilities
Liabilities
Carrying Amount	5,000		11,129
Carrying Amount | Recourse Indebtedness | Junior subordinated notes, at fair value
Liabilities
Carrying Amount	12,515		11,911
Carrying Amount | Recourse Indebtedness | Junior subordinated notes, at amortized cost
Liabilities
Carrying Amount	25,100		25,100
Carrying Amount | Recourse Indebtedness | CMBS Facilities
Liabilities
Carrying Amount	22,133		30,618
Carrying Amount | Recourse Indebtedness | CMBS securitization
Liabilities
Carrying Amount	76,951		7,131
Carrying Amount | Non-recourse indebtedness | CDO notes payable, at amortized cost
Liabilities
Carrying Amount	1,161,735		1,202,772
Carrying Amount | Non-recourse indebtedness | CDO notes payable, at fair value
Liabilities
Carrying Amount	399,448		377,235
Carrying Amount | Non-recourse indebtedness | CMBS securitization
Liabilities
Carrying Amount	89,331		100,139
Carrying Amount | Non-recourse indebtedness | Loans payable on real estate
Liabilities
Carrying Amount	299,548		171,244
Carrying Amount | Non-recourse indebtedness | Derivative Liabilities
Liabilities
Carrying Amount	102,796		113,331
Carrying Amount | Non-recourse indebtedness | Warrants and investor SARs
Liabilities
Carrying Amount	41,004		31,304
Estimated Fair Value
Assets
Commercial mortgages, mezzanine loans, other loans and preferred equity interests, Estimated Fair Value	1,185,050		1,083,118
Investments in securities and security-related receivables, Carrying Amount	573,739		567,302
Cash and cash equivalents, Estimated Fair Value	110,072		88,847
Restricted cash, Carrying Amount	92,497		121,589
Estimated Fair Value | Derivative assets
Assets
Derivative assets	946		1,305
Estimated Fair Value | 7.0% convertible senior notes
Liabilities
Convertible senior notes, Estimated Fair Value	44,626		47,778
Estimated Fair Value | 4.0% Convertible Senior Notes
Liabilities
Convertible senior notes, Estimated Fair Value	137,125		124,063
Estimated Fair Value | Junior subordinated notes, at amortized cost
Liabilities
Junior subordinated notes	14,534		14,007
Estimated Fair Value | CDO notes payable, at amortized cost
Liabilities
Notes payable, Estimated Fair Value	975,719		724,885
Estimated Fair Value | CMBS securitization
Liabilities
Notes payable, Estimated Fair Value	89,331		100,214
Estimated Fair Value | Loans payable on real estate
Liabilities
Notes payable, Estimated Fair Value	303,873		176,979
Estimated Fair Value | Recourse Indebtedness | 7.0% convertible senior notes
Liabilities
Convertible senior notes, Estimated Fair Value	44,626		47,778
Estimated Fair Value | Recourse Indebtedness | 4.0% Convertible Senior Notes
Liabilities
Convertible senior notes, Estimated Fair Value	137,125		124,063
Estimated Fair Value | Recourse Indebtedness | Secured credit facilities
Liabilities
Secured credit facilities, Estimated Fair Value	5,000		11,129
Estimated Fair Value | Recourse Indebtedness | Junior subordinated notes, at fair value
Liabilities
Junior subordinated notes	12,515		11,911
Estimated Fair Value | Recourse Indebtedness | Junior subordinated notes, at amortized cost
Liabilities
Junior subordinated notes	14,534		14,007
Estimated Fair Value | Recourse Indebtedness | CMBS Facilities
Liabilities
Carrying Amount	22,133		30,618
Estimated Fair Value | Recourse Indebtedness | CMBS securitization
Liabilities
Carrying Amount	76,951		7,131
Estimated Fair Value | Non-recourse indebtedness | CDO notes payable, at amortized cost
Liabilities
Notes payable, Estimated Fair Value	975,719		724,885
Estimated Fair Value | Non-recourse indebtedness | CDO notes payable, at fair value
Liabilities
Notes payable, Estimated Fair Value	399,448		377,235
Estimated Fair Value | Non-recourse indebtedness | CMBS securitization
Liabilities
Notes payable, Estimated Fair Value	89,331		100,214
Estimated Fair Value | Non-recourse indebtedness | Loans payable on real estate
Liabilities
Notes payable, Estimated Fair Value	303,873		176,979
Estimated Fair Value | Non-recourse indebtedness | Derivative Liabilities
Liabilities
Derivative liabilities	102,796		113,331
Estimated Fair Value | Non-recourse indebtedness | Warrants and investor SARs
Liabilities
Derivative liabilities	$ 41,004		$ 31,304

[1] Excludes senior secured notes issued by us with an aggregate principal amount equal to $84,000 with a weighted average coupon of 7.0%, which are eliminated in consolidation.

[2] Excludes senior secured notes issued by us with an aggregate principal amount equal to $86,000 with a weighted average coupon of 7.0%, which are eliminated in consolidation.