Investments in Loans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2014 Loan		Dec. 31, 2013 Loan
Mortgage Loans on Real Estate [Line Items]
Unpaid Principal Balance	$ 1,259,077		$ 1,146,574
Deferred fees	(1,916)		(800)
Total investments in loans, Unpaid Principal Balance	1,257,161		1,145,774
Total investment in loans, Unamortized (Discounts) Premiums	(22,006)		(23,397)
Carrying Amount	1,237,071		1,123,177
Commercial mortgages, mezzanine loans and other loans, Carrying Amount	1,235,155		1,122,377
Number of Loans	162		153
Weighted-Average Coupon	6.90%	[1]	7.20%	[2]
Deferred Fee
Mortgage Loans on Real Estate [Line Items]
Total investment in loans, Unamortized (Discounts) Premiums	0		0
Commercial mortgages
Mortgage Loans on Real Estate [Line Items]
Unpaid Principal Balance	927,998		792,526
Total investment in loans, Unamortized (Discounts) Premiums	(18,137)		(19,257)
Carrying Amount	909,861		773,269
Number of Loans	73		59
Weighted-Average Coupon	6.30%	[1]	6.40%	[2]
Range of Maturity Dates, Minimum	May 01, 2014		Mar. 01, 2014
Range of Maturity Dates, Maximum	Apr. 01, 2024		Jan. 01, 2029
Mezzanine Loans
Mortgage Loans on Real Estate [Line Items]
Unpaid Principal Balance	257,845		269,034
Total investment in loans, Unamortized (Discounts) Premiums	(3,021)		(3,273)
Carrying Amount	254,824		265,761
Number of Loans	77		81
Weighted-Average Coupon	9.50%	[1]	9.60%	[2]
Range of Maturity Dates, Minimum	Jun. 01, 2014		Mar. 01, 2014
Range of Maturity Dates, Maximum	Jan. 01, 2029		Jan. 01, 2029
Preferred Equity Interests
Mortgage Loans on Real Estate [Line Items]
Unpaid Principal Balance	42,609		54,389
Total investment in loans, Unamortized (Discounts) Premiums	(914)		(939)
Carrying Amount	41,695		53,450
Number of Loans	10		11
Weighted-Average Coupon	7.70%	[1]	8.60%	[2]
Range of Maturity Dates, Minimum	May 01, 2015		May 01, 2015
Range of Maturity Dates, Maximum	Aug. 01, 2025		Aug. 01, 2025
CRE Loans
Mortgage Loans on Real Estate [Line Items]
Unpaid Principal Balance	1,228,452		1,115,949
Total investment in loans, Unamortized (Discounts) Premiums	(22,072)		(23,469)
Carrying Amount	1,206,380		1,092,480
Number of Loans	160		151
Weighted-Average Coupon	7.00%	[1]	7.30%	[2]
Other loans
Mortgage Loans on Real Estate [Line Items]
Unpaid Principal Balance	30,625		30,625
Total investment in loans, Unamortized (Discounts) Premiums	66		72
Carrying Amount, Other loans	$ 30,691		$ 30,697
Number of Loans	2		2
Weighted-Average Coupon	4.30%	[1]	4.30%	[2]
Range of Maturity Dates, Minimum	Jun. 01, 2014		Mar. 01, 2014
Range of Maturity Dates, Maximum	Oct. 01, 2016		Oct. 01, 2016

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

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