Real Estate Debt Investments (Details) (USD $)	6 Months Ended	12 Months Ended	1 Months Ended		1 Months Ended					1 Months Ended	6 Months Ended	12 Months Ended		6 Months Ended	12 Months Ended	1 Months Ended	6 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended	6 Months Ended	1 Months Ended	6 Months Ended
	Jun. 30, 2013 investment	Dec. 31, 2012 investment	Apr. 30, 2013 Milford Plaza hotel item	Jun. 30, 2013 Milford Plaza hotel	Apr. 30, 2013 Milford Plaza hotel Sponsor	Jun. 30, 2013 Securitization 2012-1	Dec. 31, 2012 Securitization 2012-1	Jun. 30, 2013 Term Loan Facilities	Dec. 31, 2012 Term Loan Facilities	Apr. 30, 2013 Term Loan Facilities Milford Plaza hotel	Jun. 30, 2013 Weighted Average	Dec. 31, 2012 Weighted Average	Jun. 30, 2013 First mortgage loans, mezzanine loans and subordinate mortgage interests	Jun. 30, 2013 First mortgage loans investment	Dec. 31, 2012 First mortgage loans investment	Apr. 30, 2013 First mortgage loans Milford Plaza hotel	Jun. 30, 2013 First mortgage loans Weighted Average	Dec. 31, 2012 First mortgage loans Weighted Average	Jun. 30, 2013 Mezzanine loans investment	Dec. 31, 2012 Mezzanine loans investment	Jun. 30, 2013 Mezzanine loans Weighted Average	Dec. 31, 2012 Mezzanine loans Weighted Average	Jun. 30, 2013 Subordinate mortgage interests investment	Apr. 30, 2013 Subordinate mortgage interests Milford Plaza hotel	Jun. 30, 2013 Subordinate mortgage interests Weighted Average	Dec. 31, 2012 First mortgage / mezzanine loans
CRE debt investments
Number	29	20												26	18				2	2			1
Principal Amount	$ 945,910,000	$ 543,619,000												$ 856,160,000	$ 486,992,000				$ 56,500,000	$ 56,627,000			$ 33,250,000
Carrying Value	925,896,000	514,058,000												836,146,000	476,717,000				56,500,000	37,341,000			33,250,000
Description of variable rate	LIBOR	LIBOR												LIBOR	LIBOR				LIBOR	LIBOR			LIBOR
Fixed Rate (as a percent)											10.56%	12.47%					9.31%	13.25%			11.50%	11.50%			13.11%
Spread over LIBOR (as a percent)											6.68%	6.18%					6.66%	6.14%			10.00%	10.00%			0.00%
Unleveraged Current Yield (as a percent)											8.64%	8.50%					8.24%	8.22%			11.90%	12.12%			13.24%
Floating Rate as % of Principal Amount	79.20%	81.00%												87.20%	89.50%				8.00%	8.20%			0.00%
LIBOR floor (as a percent)											1.35%	1.61%					1.35%	1.61%			1.35%	1.61%			1.35%
Future funding commitments													21,800,000													29,800,000
Carrying value served as collateral						194,500,000	194,500,000	361,000,000	197,600,000
Amount borrowed to finance initial investment in mortgage loans originated										45,500,000
Principal amount of loans originated with the Sponsor			255,000,000
Investments financed by borrowings together with Sponsor																56,000,000								33,300,000
Number of rooms			1,331
Ownership percentage			35.00%	35.00%
Company funded investment and the Sponsor funded			$ 89,300,000		$ 165,700,000