Investments in Loans (Detail) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2016 USD ($) Loan		Dec. 31, 2015 USD ($) Loan
Mortgage Loans On Real Estate [Line Items]
Number of Loans | Loan	1
Commercial Portfolio Segment
Mortgage Loans On Real Estate [Line Items]
Unpaid Principal Balance	$ 1,496,821		$ 1,627,121
Total investment in loans, Unamortized (Discounts) Premiums	(1,171)		(1,268)
Carrying Amount	$ 1,495,650		$ 1,625,853
Number of Loans | Loan	166		188
Weighted-Average Coupon	6.10%	[1]	6.10%	[2]
Deferred fees	$ (307)		$ (2,270)
Total investments in loans, Unpaid Principal Balance	1,496,514		1,624,851
Commercial mortgages, mezzanine loans and other loans, Carrying Amount	1,495,343		1,623,583
Commercial mortgage loans | Commercial Portfolio Segment
Mortgage Loans On Real Estate [Line Items]
Unpaid Principal Balance	1,315,301	[3]	1,427,328	[4]
Total investment in loans, Unamortized (Discounts) Premiums	(952)	[3]	(1,049)	[4]
Carrying Amount	$ 1,314,349	[3]	$ 1,426,279	[4]
Number of Loans | Loan	109	[3]	124	[4]
Weighted-Average Coupon	5.70%	[1],[3]	5.20%	[2],[4]
Range of Maturity Dates, Minimum	Jul. 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 | Commercial Portfolio Segment
Mortgage Loans On Real Estate [Line Items]
Unpaid Principal Balance	$ 142,582		$ 169,556
Total investment in loans, Unamortized (Discounts) Premiums	(218)		(218)
Carrying Amount	$ 142,364		$ 169,338
Number of Loans | Loan	42		57
Weighted-Average Coupon	9.60%	[1]	10.00%	[2]
Range of Maturity Dates, Minimum	Sep. 01, 2016	[5]	Jan. 01, 2016	[6]
Range of Maturity Dates, Maximum	Jan. 01, 2029	[5]	May 01, 2025	[6]
Preferred Equity Interests | Commercial Portfolio Segment
Mortgage Loans On Real Estate [Line Items]
Unpaid Principal Balance	$ 38,938		$ 30,237
Total investment in loans, Unamortized (Discounts) Premiums	(1)		(1)
Carrying Amount	$ 38,937		$ 30,236
Number of Loans | Loan	15		7
Weighted-Average Coupon	7.50%	[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 mortgage loans includes five conduit loans with an unpaid principal balance and carrying amount of $41,455, a weighted-average coupon of 4.8% and maturity dates ranging from June 2025 through July 2026. These commercial mortgages are accounted for as loans held for sale.

[4] Commercial mortgage loans 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 seven loans all of which had maturity dates prior to June 30, 2016 and six of which have been identified as impaired. Three of these loans are 90 days or more past due, two are current and two are 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 dates prior to December 31, 2015