Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011	Dec. 31, 2010
Assets
Commercial mortgages, mezzanine loans and other loans, Carrying Amount	$ 1,046,442	$ 996,363
Investments in securities and security-related receivables, Carrying Amount	655,017	647,461
Cash and cash equivalents, Carrying Amount	40,719	29,720	29,693	27,230
Restricted cash, Carrying Amount	114,804	278,607
Derivative assets	1,026	1,360
Liabilities
Carrying Amount	1,773,204	1,748,274
Junior subordinated notes, Estimated Fair Value	22,450	22,450
CDO notes payable, Estimated Fair Value	174,422	122,506
Derivative liabilities	162,341	181,499
Recourse indebtedness [Member]
Liabilities
Carrying Amount	165,343	169,107
Non-recourse indebtedness [Member]
Liabilities
Carrying Amount	1,607,861	1,579,167
Carrying Amount [Member]
Assets
Commercial mortgages, mezzanine loans and other loans, Carrying Amount	1,046,442
Investments in securities and security-related receivables, Carrying Amount	655,016
Cash and cash equivalents, Carrying Amount	40,719
Restricted cash, Carrying Amount	114,804
Carrying Amount [Member] | 7.0% convertible senior notes [Member]
Liabilities
Carrying Amount	109,229
Carrying Amount [Member] | Junior subordinated notes, at amortized cost [Member]
Liabilities
Carrying Amount	25,100
Carrying Amount [Member] | CDO notes payable, at amortized cost [Member]
Liabilities
Carrying Amount	1,298,640
Carrying Amount [Member] | Loans payable on real estate [Member]
Liabilities
Carrying Amount	134,799
Carrying Amount [Member] | Derivative assets [Member]
Assets
Derivative assets	1,026
Carrying Amount [Member] | Recourse indebtedness [Member] | 7.0% convertible senior notes [Member]
Liabilities
Carrying Amount	109,229
Carrying Amount [Member] | Recourse indebtedness [Member] | Secured credit facility [Member]
Liabilities
Carrying Amount	8,564
Carrying Amount [Member] | Recourse indebtedness [Member] | Junior subordinated notes, at fair value [Member]
Liabilities
Carrying Amount	22,450
Carrying Amount [Member] | Recourse indebtedness [Member] | Junior subordinated notes, at amortized cost [Member]
Liabilities
Carrying Amount	25,100
Carrying Amount [Member] | Non-recourse indebtedness [Member] | CDO notes payable, at amortized cost [Member]
Liabilities
Carrying Amount	1,298,640
Carrying Amount [Member] | Non-recourse indebtedness [Member] | CDO notes payable, at fair value [Member]
Liabilities
Carrying Amount	174,422
Carrying Amount [Member] | Non-recourse indebtedness [Member] | Loans payable on real estate [Member]
Liabilities
Carrying Amount	134,799
Carrying Amount [Member] | Non-recourse indebtedness [Member] | Derivative Liabilities [Member]
Liabilities
Carrying Amount	162,341
Estimated Fair Value [Member]
Assets
Commercial mortgages, mezzanine loans and other loans, Estimated Fair Value	1,035,913
Investments in securities and security-related receivables, Carrying Amount	655,016
Cash and cash equivalents, Estimated Fair Value	40,719
Restricted cash, Carrying Amount	114,804
Estimated Fair Value [Member] | 7.0% convertible senior notes [Member]
Liabilities
Convertible senior notes, Estimated Fair Value	113,275
Estimated Fair Value [Member] | Junior subordinated notes, at amortized cost [Member]
Liabilities
Junior subordinated notes, Estimated Fair Value	14,809
Estimated Fair Value [Member] | CDO notes payable, at amortized cost [Member]
Liabilities
CDO notes payable, Estimated Fair Value	724,633
Estimated Fair Value [Member] | Loans payable on real estate [Member]
Liabilities
Loans payable on real estate, Estimated Fair Value	148,384
Estimated Fair Value [Member] | Derivative assets [Member]
Assets
Derivative assets	1,026
Estimated Fair Value [Member] | Recourse indebtedness [Member] | 7.0% convertible senior notes [Member]
Liabilities
Convertible senior notes, Estimated Fair Value	113,275
Estimated Fair Value [Member] | Recourse indebtedness [Member] | Secured credit facility [Member]
Liabilities
Secured credit facilities, Estimated Fair Value	8,564
Estimated Fair Value [Member] | Recourse indebtedness [Member] | Junior subordinated notes, at fair value [Member]
Liabilities
Carrying Amount	22,450
Estimated Fair Value [Member] | Recourse indebtedness [Member] | Junior subordinated notes, at amortized cost [Member]
Liabilities
Junior subordinated notes, Estimated Fair Value	14,809
Estimated Fair Value [Member] | Non-recourse indebtedness [Member] | CDO notes payable, at amortized cost [Member]
Liabilities
CDO notes payable, Estimated Fair Value	724,633
Estimated Fair Value [Member] | Non-recourse indebtedness [Member] | CDO notes payable, at fair value [Member]
Liabilities
Carrying Amount	174,422
Estimated Fair Value [Member] | Non-recourse indebtedness [Member] | Loans payable on real estate [Member]
Liabilities
Loans payable on real estate, Estimated Fair Value	148,384
Estimated Fair Value [Member] | Non-recourse indebtedness [Member] | Derivative Liabilities [Member]
Liabilities
Carrying Amount	$ 162,341