Loans (Details) (USD $)	12 Months Ended																											12 Months Ended						12 Months Ended					1 Months Ended	12 Months Ended					12 Months Ended						12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 California unit	Dec. 31, 2011 Northern Virginia unit	Dec. 31, 2011 U.S unit	Dec. 31, 2011 North Carolina	Dec. 31, 2011 Pennsylvania unit	Dec. 31, 2011 1-month LIBOR	Dec. 31, 2010 1-month LIBOR	Dec. 31, 2011 3-month LIBOR	Dec. 31, 2010 3-month LIBOR	Dec. 31, 2011 One-month Citibank LIBOR	Dec. 31, 2011 Three-month Citibank LIBOR	Dec. 31, 2011 Six-month Citibank LIBOR	Dec. 31, 2011 LIBOR floor	Dec. 31, 2011 Rating 1 Maximum	Dec. 31, 2011 Rating 2	Dec. 31, 2011 Rating 2 Maximum	Dec. 31, 2011 Rating 3	Dec. 31, 2011 Rating 3 Maximum	Dec. 31, 2011 Rating 4	Dec. 31, 2011 Rating 4 Minimum	Dec. 31, 2011 Rating 4 Maximum	Dec. 31, 2011 Rating 5 Minimum	Dec. 31, 2011 Total loans held for investment	Dec. 31, 2010 Total loans held for investment	Dec. 31, 2011 First Mortgages: Y	Dec. 31, 2010 First Mortgages: Y	Dec. 31, 2011 First Mortgages: Northern Virginia	Dec. 31, 2011 First Mortgages: Rating 2	Dec. 31, 2011 First Mortgages: Rating 3	Dec. 31, 2011 First Mortgages: Rating 4	Dec. 31, 2011 Subordinated mortgages Y	Dec. 31, 2010 Subordinated mortgages Y	Dec. 31, 2011 Subordinated mortgages Rating 2	Dec. 31, 2011 Subordinated mortgages Rating 3	Dec. 31, 2011 Subordinated mortgages Rating 4	Feb. 29, 2012 Mezzanine Loans unit	Dec. 31, 2011 Mezzanine Loans Y	Dec. 31, 2010 Mezzanine Loans Y	Dec. 31, 2011 Mezzanine Loans Rating 2	Dec. 31, 2011 Mezzanine Loans Rating 3	Dec. 31, 2011 Mezzanine Loans Rating 4	Dec. 31, 2011 Commercial mortgage loans unit	Dec. 31, 2011 A-note unit	Dec. 31, 2011 First mortgages held for sale at fair value Y	Dec. 31, 2010 First mortgages held for sale at fair value Y	Dec. 31, 2011 First mortgages held for sale at fair value Rating 2	Dec. 31, 2011 First mortgages held for sale at fair value Rating 3	Dec. 31, 2011 Loans held in securitization trust Y	Dec. 31, 2010 Loans held in securitization trust Y	Dec. 31, 2011 Loans held in securitization trust Rating 2	Dec. 31, 2011 Loans held in securitization trust Rating 3
Investments in loans
Loans with variable rates of interest	$ 1,100,000,000	$ 332,700,000							$ 264,000,000	$ 211,500,000	$ 143,400,000	$ 121,200,000	$ 134,000,000	$ 7,100,000	$ 6,000,000	$ 551,300,000
Face amount of new loans	1,800,000,000				188,000,000	137,800,000
Carrying Value	2,447,508,000	1,425,243,000																482,301,000		1,864,443,000		100,764,000				2,268,599,000	1,230,783,000	1,202,611,000	757,684,000		108,900,000	1,054,717,000	38,994,000	437,163,000	406,410,000	131,281,000	251,788,000	54,094,000		628,825,000	66,689,000	139,167,000	481,982,000	7,676,000			128,593,000	144,163,000	89,760,000	38,833,000	50,316,000	50,297,000	13,193,000	37,123,000
Acquisitions/Origination	1,782,964,000	1,352,253,000	215,048,000	165,500,000	156,500,000	127,100,000	175,000,000	60,500,000																						34,500,000									40,000,000							185,000,000
Face value	2,552,020,000	1,525,605,000																								2,378,555,000	1,330,966,000	1,248,549,000	797,154,000					487,175,000	465,929,000					642,831,000	67,883,000				333,000,000		122,833,000	143,901,000			50,632,000	50,738,000
Weighted Average Coupon (as a percent)																												6.60%	6.90%					7.40%	6.60%					8.40%	10.80%						5.90%	5.70%			5.00%	5.00%
WAL (in years)																												3.2	3.3					4.1	4.9					3.0	4.8						8.9	4.9			3.7	4.2
Loans with variable rates of interest (as a percent)	45.20%	23.30%
Variable rate basis of loans	LIBOR	LIBOR							one-month LIBOR	one-month LIBOR	three-month LIBOR	three-month LIBOR	one-month Citibank LIBOR	three-month Citibank LIBOR	six-month Citibank LIBOR
Weighted average spread of loans (as a percent)	4.33%	2.30%
Effective variable rate basis (as a percent)									0.2953%	0.2606%	0.581%	0.3028%	0.27%	0.56%	0.78%
LTV (as a percent)																	65.00%		70.00%		80.00%		80.00%	90.00%
Threshold LTV (as a percent)																									90.00%
Number of properties collateralizing loans originated or acquired				6	10	28		2																															10						26	143
Interest acquired in mezzanine loan (as a percent)					90.00%
Movement of loans held for investment
Beginning Balance	1,425,243,000	214,521,000
Acquisitions/Origination	1,782,964,000	1,352,253,000	215,048,000	165,500,000	156,500,000	127,100,000	175,000,000	60,500,000																						34,500,000									40,000,000							185,000,000
Additional funding	45,792,000		305,000
Capitalized interest	7,485,000	3,323,000
Basis of loans sold	(331,312,000)	(28,911,000)
Loan maturities	(305,316,000)	(114,717,000)
Transfer out - loan converted to a security	(176,635,000)
Principal repayments	(26,933,000)	(13,642,000)	(1,150,000)
Discount accretion /premium amortization	26,966,000	6,339,000	318,000
Unrealized foreign currency remeasurement gain (loss)	(6,506,000)	6,077,000
Unrealized gains on loans held for sale at fair value	5,760,000
Balance at the end of the period	$ 2,447,508,000	$ 1,425,243,000	$ 214,521,000