CRE Debt and Preferred Equity Investments -Based on Outstanding Principal (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013
Transaction to Real Estate Investments [Line Items]
Beginning principal balance, net of loss reserves	$ 727,078
Purchases/advances (principal)	988,847
Sales (principal)	(13,750)
Remaining premium (discount)	1,660
Principal payments	(114,976)
Allowance for loan losses
Net carrying value (excluding origination fees)	1,588,859
Commercial Mortgage
Transaction to Real Estate Investments [Line Items]
Net carrying value (excluding origination fees)	1,588,859
Commercial Mortgage | Senior Mortgages
Transaction to Real Estate Investments [Line Items]
Beginning principal balance, net of loss reserves	100,907
Purchases/advances (principal)	594,143
Sales (principal)	(13,750)
Remaining premium (discount)	458
Principal payments	(24,309)
Transfers	12,500
Allowance for loan losses
Net carrying value (excluding origination fees)	669,949
Commercial Mortgage | Subordinated Notes
Transaction to Real Estate Investments [Line Items]
Beginning principal balance, net of loss reserves	41,293
Remaining premium (discount)	350
Principal payments	(235)
Allowance for loan losses
Net carrying value (excluding origination fees)	41,408
Commercial Mortgage | Mezzanine Loans
Transaction to Real Estate Investments [Line Items]
Beginning principal balance, net of loss reserves	545,109
Purchases/advances (principal)	184,704
Remaining premium (discount)	1,476
Principal payments	(90,432)
Transfers	(12,500)
Allowance for loan losses
Net carrying value (excluding origination fees)	628,357
Commercial Mortgage | Preferred Equity Interests
Transaction to Real Estate Investments [Line Items]
Beginning principal balance, net of loss reserves	39,769
Purchases/advances (principal)	210,000
Remaining premium (discount)	(624)
Allowance for loan losses
Net carrying value (excluding origination fees)	$ 249,145