Loans - Held for Investment (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Dec. 31, 2014
Investments in loans
Total gross loans	$ 6,031,123	$ 6,269,546
Loan loss allowance (loans held-for-investment)	(7,297)	(6,029)	$ (9,009)	$ (6,031)
Carrying Value	6,023,826	6,263,517
Face Amount	6,092,193	6,335,023
Loans with variable rates of interest	$ 5,080,421	5,052,055
Loans with variable rates of interest (as a percent)	89.10%
Weighted average spread of loans (as a percent)	5.90%
1-month LIBOR
Investments in loans
Loans with variable rates of interest	$ 572,062	$ 438,641
Effective variable rate basis (as a percent)	0.4651%	0.4295%
3-month LIBOR
Investments in loans
Loans with variable rates of interest		$ 375,467
Effective variable rate basis (as a percent)		0.5904%
LIBOR floor
Investments in loans
Loans with variable rates of interest	$ 4,508,359	$ 4,237,947
LIBOR floor | Weighted-average
Investments in loans
Effective variable rate basis (as a percent)	0.32%	0.31%
LIBOR floor | Minimum
Investments in loans
Effective variable rate basis (as a percent)	0.15%	0.15%
LIBOR floor | Maximum
Investments in loans
Effective variable rate basis (as a percent)	3.00%	3.00%
Total loans held-for-investment
Investments in loans
Total gross loans	$ 5,700,749	$ 5,979,108
Face Amount	5,762,229	6,043,313
Loans held-for-sale
Investments in loans
Total gross loans	237,106	203,865
Face Amount	$ 235,296	$ 203,710
Weighted Average Coupon (as a percent)	5.00%	4.90%
Weighted Average Life	9 years 9 months 18 days	9 years 9 months 18 days
Loans transferred as secured borrowings
Investments in loans
Total gross loans	$ 93,268	$ 86,573
Face Amount	$ 94,668	$ 88,000
Weighted Average Coupon (as a percent)	6.10%	6.10%
Weighted Average Life	2 years	2 years 4 months 24 days
First Mortgages: | Total loans held-for-investment
Investments in loans
Total gross loans	$ 4,538,986	$ 4,723,852
Face Amount	$ 4,592,601	$ 4,776,576
Weighted Average Coupon (as a percent)	5.80%	6.00%
Weighted Average Life	2 years 4 months 24 days	2 years 8 months 12 days
Subordinated mortgages | Total loans held-for-investment
Investments in loans
Total gross loans	$ 392,208	$ 392,563
Face Amount	$ 413,228	$ 416,713
Weighted Average Coupon (as a percent)	8.50%	8.50%
Weighted Average Life	3 years	3 years 4 months 24 days
Mezzanine Loans
Investments in loans
Carrying Value	$ 949,200	$ 930,000
Mezzanine Loans | Total loans held-for-investment
Investments in loans
Total gross loans	769,555	862,693
Face Amount	$ 756,400	$ 850,024
Weighted Average Coupon (as a percent)	9.90%	9.90%
Weighted Average Life	2 years 1 month 6 days	2 years 6 months