Investments in Loans (Parenthetical) (Detail) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2016 USD ($) Loan		Dec. 31, 2015 USD ($) Loan
Mortgage Loans On Real Estate [Line Items]
Number of Loans	1
Unpaid Principal Balance | $	$ 1,614,712		$ 1,627,121
Mezzanine Loans
Mortgage Loans On Real Estate [Line Items]
Number of Loans	54		57
Unpaid Principal Balance | $	$ 169,415		$ 169,556
Weighted-Average Coupon	9.80%	[1]	10.00%	[2]
Mezzanine Loans | Impaired Loans
Mortgage Loans On Real Estate [Line Items]
Number of Loans	5
Mezzanine Loans | 90 days or more
Mortgage Loans On Real Estate [Line Items]
Number of Loans	3		3
Mezzanine Loans | 30 to 59 days
Mortgage Loans On Real Estate [Line Items]
Number of Loans	1
Mezzanine Loans | Loans to be Restructured
Mortgage Loans On Real Estate [Line Items]
Number of Loans	1
Conduit Loans
Mortgage Loans On Real Estate [Line Items]
Number of Loans	7		6
Unpaid Principal Balance | $	$ 57,928		$ 49,239
Weighted-Average Coupon	4.90%		4.80%

[1] Weighted-average coupon is calculated on the unpaid principal balance, which does not necessarily correspond to the carrying amount.

[2] Weighted-average coupon is calculated on the unpaid principal balance, which does not necessarily correspond to the carrying amount.