Investments in Loans (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]
Unpaid Principal Balance	$ 1,614,712		$ 1,627,121
Total investment in loans, Unamortized (Discounts) Premiums	$ (1,220)		(1,268)
Number of Loans | Loan	1
Deferred fees	$ (860)		(2,270)
Total investments in loans, Unpaid Principal Balance	1,613,852		1,624,851
Commercial mortgages, mezzanine loans and other loans, Carrying Amount	1,612,632		1,623,583
CRE Loans
Mortgage Loans On Real Estate [Line Items]
Unpaid Principal Balance	1,614,712		1,627,121
Total investment in loans, Unamortized (Discounts) Premiums	(1,220)		(1,268)
Carrying Amount	$ 1,613,492		$ 1,625,853
Number of Loans | Loan	181		188
Weighted-Average Coupon	6.00%	[1]	6.10%	[2]
Commercial mortgages
Mortgage Loans On Real Estate [Line Items]
Unpaid Principal Balance	$ 1,421,060	[3]	$ 1,427,328	[4]
Total investment in loans, Unamortized (Discounts) Premiums	(1,001)	[3]	(1,049)	[4]
Carrying Amount	$ 1,420,059	[3]	$ 1,426,279	[4]
Number of Loans | Loan	121	[3]	124	[4]
Weighted-Average Coupon	5.60%	[1],[3]	5.20%	[2],[4]
Range of Maturity Dates, Minimum	Apr. 01, 2016	[3],[5]	Mar. 01, 2016	[4],[6]
Range of Maturity Dates, Maximum	Jan. 01, 2029	[3],[5]	Jan. 01, 2029	[4],[6]
Mezzanine Loans
Mortgage Loans On Real Estate [Line Items]
Unpaid Principal Balance	$ 169,415		$ 169,556
Total investment in loans, Unamortized (Discounts) Premiums	(218)		(218)
Carrying Amount	$ 169,197		$ 169,338
Number of Loans | Loan	54		57
Weighted-Average Coupon	9.80%	[1]	10.00%	[2]
Range of Maturity Dates, Minimum	May 01, 2016	[5]	Jan. 01, 2016	[6]
Range of Maturity Dates, Maximum	May 01, 2025	[5]	May 01, 2025	[6]
Preferred Equity Interests
Mortgage Loans On Real Estate [Line Items]
Unpaid Principal Balance	$ 24,237		$ 30,237
Total investment in loans, Unamortized (Discounts) Premiums	(1)		(1)
Carrying Amount	$ 24,236		$ 30,236
Number of Loans | Loan	6		7
Weighted-Average Coupon	5.90%	[1]	6.90%	[2]
Range of Maturity Dates, Minimum	Sep. 01, 2016	[5]	Feb. 01, 2016	[6]
Range of Maturity Dates, Maximum	Aug. 01, 2025	[5]	Aug. 01, 2025	[6]

[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.

[3] Commercial mortgages includes seven conduit loans with an unpaid principal balance and carrying amount of $57,928, a weighted-average coupon of 4.9% and maturity dates ranging from December 2020 through February 2026. These commercial mortgages are accounted for as loans held for sale.

[4] Commercial mortgages includes six conduit loans with an unpaid principal balance and carrying amount of $49,239, a weighted-average coupon of 4.8% and maturity dates ranging from December 2020 through January 2026. These commercial mortgages are accounted for as loans held for sale.

[5] Does not include the maturity dates of five mezzanine loans all of which had maturity dates prior to March 31, 2016 and have been identified as impaired. Three of these loans are 90 days or more past due, one of these loans is 30 to 59 days past due and one of these loans is in the process of being restructured.

[6] Does not include the maturity dates of three mezzanine loans that were 90 days or more past due which had contractual maturity date prior to December 31, 2015.