Fair Value of Financial Instruments (Details 3) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Carrying Amount:
Commercial mortgages, mezzanine loans and other loans, Carrying Amount	$ 1,090,481	$ 996,363
Debt, Carrying Amount	1,785,358	1,748,274
Estimated Fair Value:
Junior subordinated notes, Estimated Fair Value	22,450
CDO notes payable, Estimated Fair Value	159,077
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Estimated Fair Value:
Commercial mortgages, mezzanine loans and other loans, Estimated Fair Value	0
Junior subordinated notes, Estimated Fair Value	0
CDO notes payable, Estimated Fair Value	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | 7.0% convertible senior notes [Member]
Estimated Fair Value:
Convertible senior notes, Estimated Fair Value	93,725
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Junior subordinated notes, at amortized cost [Member]
Estimated Fair Value:
Junior subordinated notes, Estimated Fair Value	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | CDO notes payable, at amortized cost [Member]
Estimated Fair Value:
CDO notes payable, Estimated Fair Value	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Loan Payable On Real Estate [Member]
Estimated Fair Value:
Loans payable on real estate, Estimated Fair Value	0
Significant Other Observable Inputs (Level 2) [Member]
Estimated Fair Value:
Commercial mortgages, mezzanine loans and other loans, Estimated Fair Value	0
Junior subordinated notes, Estimated Fair Value	0
CDO notes payable, Estimated Fair Value	0
Significant Other Observable Inputs (Level 2) [Member] | 7.0% convertible senior notes [Member]
Estimated Fair Value:
Convertible senior notes, Estimated Fair Value	0
Significant Other Observable Inputs (Level 2) [Member] | Junior subordinated notes, at amortized cost [Member]
Estimated Fair Value:
Junior subordinated notes, Estimated Fair Value	0
Significant Other Observable Inputs (Level 2) [Member] | CDO notes payable, at amortized cost [Member]
Estimated Fair Value:
CDO notes payable, Estimated Fair Value	0
Significant Other Observable Inputs (Level 2) [Member] | Loan Payable On Real Estate [Member]
Estimated Fair Value:
Loans payable on real estate, Estimated Fair Value	0
Significant Unobservable (Level 3) [Member]
Estimated Fair Value:
Commercial mortgages, mezzanine loans and other loans, Estimated Fair Value	1,055,388
Junior subordinated notes, Estimated Fair Value	22,450
CDO notes payable, Estimated Fair Value	159,077
Significant Unobservable (Level 3) [Member] | 7.0% convertible senior notes [Member]
Estimated Fair Value:
Convertible senior notes, Estimated Fair Value	0
Significant Unobservable (Level 3) [Member] | Junior subordinated notes, at amortized cost [Member]
Estimated Fair Value:
Junior subordinated notes, Estimated Fair Value	14,809
Significant Unobservable (Level 3) [Member] | CDO notes payable, at amortized cost [Member]
Estimated Fair Value:
CDO notes payable, Estimated Fair Value	730,372
Significant Unobservable (Level 3) [Member] | Loan Payable On Real Estate [Member]
Estimated Fair Value:
Loans payable on real estate, Estimated Fair Value	148,669
Carrying Amount [Member]
Carrying Amount:
Commercial mortgages, mezzanine loans and other loans, Carrying Amount	1,090,481
Carrying Amount [Member] | 7.0% convertible senior notes [Member]
Carrying Amount:
Debt, Carrying Amount	108,827
Carrying Amount [Member] | Junior subordinated notes, at amortized cost [Member]
Carrying Amount:
Debt, Carrying Amount	25,100
Carrying Amount [Member] | CDO notes payable, at amortized cost [Member]
Carrying Amount:
Debt, Carrying Amount	1,306,977
Carrying Amount [Member] | Loan Payable On Real Estate [Member]
Carrying Amount:
Debt, Carrying Amount	135,074
Estimated Fair Value [Member]
Estimated Fair Value:
Commercial mortgages, mezzanine loans and other loans, Estimated Fair Value	1,055,388
Estimated Fair Value [Member] | 7.0% convertible senior notes [Member]
Estimated Fair Value:
Convertible senior notes, Estimated Fair Value	93,725
Estimated Fair Value [Member] | Junior subordinated notes, at amortized cost [Member]
Estimated Fair Value:
Junior subordinated notes, Estimated Fair Value	14,809
Estimated Fair Value [Member] | CDO notes payable, at amortized cost [Member]
Estimated Fair Value:
CDO notes payable, Estimated Fair Value	730,372
Estimated Fair Value [Member] | Loan Payable On Real Estate [Member]
Estimated Fair Value:
Loans payable on real estate, Estimated Fair Value	$ 148,669