Borrowings (Details) (USD $)	1 Months Ended	6 Months Ended			1 Months Ended						1 Months Ended							6 Months Ended					6 Months Ended					6 Months Ended
	Aug. 31, 2013 investment	Jun. 30, 2014 investment	Jun. 30, 2013	Dec. 31, 2013	Aug. 31, 2013 Securitization 2013-1	Aug. 31, 2013 Securitization 2013-1 investment	Nov. 30, 2012 Securitization 2012-1 investment	Aug. 31, 2013 Senior Loans investment	Jun. 30, 2014 Loan Facilities loan	Jun. 30, 2014 Loan Facilities CRE debt investments	Nov. 30, 2012 Loan Facilities Securitization 2012-1	Feb. 28, 2012 Loan Facility 1	Jun. 30, 2014 Loan Facility 2	Dec. 31, 2013 Loan Facility 2	Apr. 30, 2013 Loan Facility 2	Nov. 30, 2012 Loan Facility 2	Jul. 31, 2012 Loan Facility 2	Jun. 30, 2014 Loan Facility 2 Minimum	Jun. 30, 2014 Loan Facility 2 Maximum	Jun. 30, 2014 Loan Facility 3	Dec. 31, 2013 Loan Facility 3	Jul. 31, 2012 Loan Facility 3	Jun. 30, 2014 Loan Facility 3 Minimum	Jun. 30, 2014 Loan Facility 3 Maximum	Jun. 30, 2014 Loan Facility 4	Dec. 31, 2013 Loan Facility 4	Mar. 31, 2013 Loan Facility 4	Jun. 30, 2014 Loan Facility 4 Minimum	Jun. 30, 2014 Loan Facility 4 Maximum	Jun. 30, 2014 CMBS Facilities	Dec. 31, 2013 CMBS Facilities	Sep. 30, 2012 CMBS Facilities agreement	Jun. 30, 2014 Securitization 2013-2	Dec. 31, 2013 Securitization 2013-2	Jun. 30, 2014 Securities Investment
Debt Instrument [Line Items]
Number of securitization financing transactions entered (investments)		2
Principal amount of investments financed by borrowings					$ 531,500,000		$ 351,400,000			$ 251,700,000
Number of CRE debt investments contributed (investments)	4					8	9	3
Aggregate principal amount of CRE debt investment contributed	105,500,000					346,100,000	199,200,000
Debt instrument debt created from bifurcation								79,100,000
Value of bonds issued	382,700,000						227,500,000
Advance rates (as a percent)	72.00%						65.00%
Interest rate margin (as a percent)					2.68%		1.77%											2.00%	4.00%				3.95%	5.95%				2.50%	3.00%
Amount of borrowings repaid	222,700,000	7,638,000	0								117,700,000
Equity interest retained in CRE debt investments contributed							70,000,000
Value of bonds used to finance the assets contributed							129,500,000
Maximum borrowing capacity												100,000,000.0			150,000,000.0	100,000,000.0	50,000,000.0					40,000,000.0					200,000,000.0
Unrestricted cash or cash equivalents required to be maintained under financial covenants																		3,800,000.0	22,500,000.0				3,800,000.0	7,500,000.0				20,000,000.0
Number of facilities (loans)									3
Carrying Value		783,385,000		637,752,000					157,600,000				51,000,000	0						9,000,000	16,638,000				97,598,000	0				11,685,000	11,685,000		100,423,000	124,679,000
Number of master repurchase agreements entered into (agreements)																																2
Real estate securities, available for sale		70,500,000		66,450,000																															17,700,000
Amount outstanding																																			$ 11,700,000