CRE Debt and Preferred Equity Investments -Based on Outstanding Principal (Detail) - USD ($) $ in Thousands		6 Months Ended	12 Months Ended
		Jun. 30, 2016	Dec. 31, 2015
Transaction to Real Estate Investments [Line Items]
Beginning balance		$ 1,348,817	$ 1,518,165
Originations & advances (principal)		190,865	489,237
Principal payments		(402,458)	(625,642)
Sales (principal)			(46,945)
Amortization & accretion of (premium) discounts		(271)	143
Net (increase) decrease in origination fees		(1,848)	(8,787)
Amortization of net origination fees		2,866	4,146
Transfers			18,500
Allowance for loan losses		0	0
Net carrying value	[1]	1,137,971	1,348,817
Preferred Equity Interests
Transaction to Real Estate Investments [Line Items]
Beginning balance		121,773	212,905
Principal payments		(113,444)	(92,210)
Amortization & accretion of (premium) discounts			517
Amortization of net origination fees		629	561
Allowance for loan losses		0	0
Net carrying value	[1]	8,958	121,773
Commercial Mortgage
Transaction to Real Estate Investments [Line Items]
Allowance for loan losses		0	0
Net carrying value	[1],[2]	1,137,971	1,348,817
Commercial Mortgage | Mezzanine Loans
Transaction to Real Estate Investments [Line Items]
Beginning balance		578,503	522,731
Originations & advances (principal)		32,363	195,312
Principal payments		(148,111)	(153,693)
Amortization & accretion of (premium) discounts		(205)	(232)
Net (increase) decrease in origination fees		(282)	(4,806)
Amortization of net origination fees		1,239	691
Transfers			18,500
Allowance for loan losses		0	0
Net carrying value	[1],[2]	463,507	578,503
Commercial Mortgage | Senior Mortgages
Transaction to Real Estate Investments [Line Items]
Beginning balance		385,838	383,895
Originations & advances (principal)		158,502	293,925
Principal payments		(65,153)	(243,270)
Sales (principal)			(46,945)
Amortization & accretion of (premium) discounts		(66)	(142)
Net (increase) decrease in origination fees		(1,566)	(3,702)
Amortization of net origination fees		705	2,077
Allowance for loan losses		0	0
Net carrying value	[1],[2]	478,260	385,838
Commercial Mortgage | Senior Securitized Mortgages
Transaction to Real Estate Investments [Line Items]
Beginning balance	[3]	262,703	398,634
Principal payments	[3]	(75,750)	(136,469)
Net (increase) decrease in origination fees	[3]		(279)
Amortization of net origination fees	[3]	293	817
Allowance for loan losses	[3]	0	0
Net carrying value	[1],[2],[3],[4]	187,246	262,703
Commercial Mortgage | Preferred Equity Interests
Transaction to Real Estate Investments [Line Items]
Net carrying value	[2]	$ 8,958	$ 121,773

[1] Excludes Loans held for sale, net.

[2] Carrying value includes unamortized origination fees of $5.9 million and $6.9 million as of June 30, 2016 and December 31, 2015, respectively.

[3] Assets of consolidated VIE.

[4] Assets of consolidated VIEs.