Loans (Details) (USD $)	9 Months Ended	12 Months Ended	9 Months Ended					0 Months Ended												9 Months Ended		9 Months Ended					9 Months Ended	12 Months Ended	9 Months Ended													9 Months Ended	12 Months Ended							9 Months Ended	12 Months Ended										9 Months Ended			12 Months Ended					9 Months Ended	0 Months Ended	9 Months Ended							0 Months Ended	9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 LNR	Sep. 30, 2013 1-month LIBOR	Dec. 31, 2012 1-month LIBOR	Dec. 31, 2012 One-month Citibank LIBOR	Dec. 31, 2012 Three-month Citibank LIBOR	Sep. 13, 2013 3 Month EURIBOR	Sep. 30, 2013 3 Month EURIBOR	Sep. 30, 2013 LIBOR floor	Dec. 31, 2012 LIBOR floor	Sep. 30, 2013 LIBOR floor Minimum	Dec. 31, 2012 LIBOR floor Minimum	Sep. 30, 2013 LIBOR floor Maximum	Dec. 31, 2012 LIBOR floor Maximum	Sep. 30, 2013 Rating 2	Dec. 31, 2012 Rating 2	Sep. 30, 2013 Rating 3	Dec. 31, 2012 Rating 3	Sep. 30, 2013 Rating 4	Dec. 31, 2012 Rating 4	Sep. 30, 2013 Rating 5	Dec. 31, 2012 Rating 5	Sep. 30, 2013 Not Rated	Sep. 30, 2013 Total loans held-for-investment item	Dec. 31, 2012 Total loans held-for-investment	Sep. 30, 2013 First Mortgages:	Dec. 31, 2012 First Mortgages:	Sep. 30, 2013 First Mortgages: LNR item	Sep. 30, 2013 First Mortgages: New York Condominium residences and ground floor retail item	Sep. 30, 2013 First Mortgages: Boston's Seaport District sqft	Sep. 30, 2013 First Mortgages: Boston's Seaport District Parking lots item	Sep. 30, 2013 First Mortgages: Boston's Seaport District Spaces item	Sep. 30, 2013 First Mortgages: Rating 2	Dec. 31, 2012 First Mortgages: Rating 2	Sep. 30, 2013 First Mortgages: Rating 3	Dec. 31, 2012 First Mortgages: Rating 3	Sep. 30, 2013 First Mortgages: Rating 4	Dec. 31, 2012 First Mortgages: Rating 4	Dec. 31, 2012 First Mortgages: Rating 5	Sep. 30, 2013 First Mortgages: Not Rated	Sep. 30, 2013 Subordinated mortgages	Dec. 31, 2012 Subordinated mortgages	Sep. 30, 2013 Subordinated mortgages Rating 2	Dec. 31, 2012 Subordinated mortgages Rating 2	Sep. 30, 2013 Subordinated mortgages Rating 3	Dec. 31, 2012 Subordinated mortgages Rating 3	Sep. 30, 2013 Subordinated mortgages Rating 4	Dec. 31, 2012 Subordinated mortgages Rating 4	Sep. 30, 2013 Mezzanine Loans	Dec. 31, 2012 Mezzanine Loans	Sep. 30, 2013 Mezzanine Loans Rating 2	Dec. 31, 2012 Mezzanine Loans Rating 2	Sep. 30, 2013 Mezzanine Loans Rating 3	Dec. 31, 2012 Mezzanine Loans Rating 3	Sep. 30, 2013 Mezzanine Loans Rating 4	Dec. 31, 2012 Mezzanine Loans Rating 4	Sep. 30, 2013 Loans Held-for-sale	Sep. 30, 2013 Loans Held-for-sale Rating 2	Sep. 30, 2013 Loans Held-for-sale Not Rated	Sep. 30, 2013 First mortgages held-for-sale, lower of cost or fair value	Sep. 30, 2013 First mortgages held-for-sale, fair value option elected	Sep. 30, 2013 Loans transferred as secured borrowings	Dec. 31, 2012 Loans transferred as secured borrowings	Sep. 30, 2013 Loans transferred as secured borrowings Rating 2	Dec. 31, 2012 Loans transferred as secured borrowings Rating 2	Sep. 30, 2013 Loans transferred as secured borrowings Rating 3	Dec. 31, 2012 Loans transferred as secured borrowings Rating 3	Sep. 30, 2013 Loans prepaid loan	Aug. 12, 2013 First mortgage and mezzanine loan loan	Sep. 30, 2013 First mortgage and mezzanine loan New York	Sep. 30, 2013 First mortgage and mezzanine loan New York Office building	Sep. 30, 2013 First mortgage and mezzanine loan Burbank, CA	Sep. 30, 2013 First mortgage and mezzanine loan San Jose, CA item	Sep. 30, 2013 Recapitalization of existing loan with first mortgage	Sep. 30, 2013 First Mortgages loan with strategic partner	Sep. 30, 2013 A-note	Sep. 13, 2013 EUR-denominated first mortgage loan item	Sep. 30, 2013 EUR-denominated first mortgage loan Manager	Sep. 30, 2013 EUR-denominated first mortgage loan Finland Manager item
Investments in loans
Loans with variable rates of interest	$ 2,708,997,000	$ 1,918,182,000		$ 453,690,000	$ 674,327,000	$ 93,195,000	$ 7,217,000		$ 54,091,000	$ 2,201,216,000	$ 1,143,443,000
Face amount of new loans	2,500,000,000																										275,000,000			86,000,000	112,000,000																																								350,000,000	158,500,000	145,600,000	136,800,000	140,000,000	142,500,000
Total gross loans	4,224,967,000	3,002,396,000														384,759,000	425,952,000	3,288,236,000	2,465,889,000	265,068,000	99,048,000		11,507,000	286,904,000	3,794,238,000	2,916,495,000	1,928,052,000	1,461,666,000						25,473,000	39,734,000	1,740,951,000	1,350,455,000	153,845,000	59,970,000	11,507,000	7,783,000	523,393,000	397,159,000	2,422,000	2,434,000	489,430,000	363,275,000	31,541,000	31,450,000	1,342,793,000	1,057,670,000	343,818,000	370,671,000	919,293,000	679,371,000	79,682,000	7,628,000	345,139,000	66,018,000	279,121,000	66,018,000	279,121,000	85,590,000	85,901,000	13,046,000	13,113,000	72,544,000	72,788,000
Loan loss allowance	(3,976,000)	(2,061,000)
Carrying Value	4,220,991,000	3,000,335,000																																																																			147,500,000
Number of loans in default																									0
Face value	4,316,819,000	3,099,060,000																							3,890,969,000	3,012,723,000	1,975,959,000	1,502,382,000														560,147,000	430,444,000							1,354,863,000	1,079,897,000										67,000,000	273,110,000	85,740,000	86,337,000
Weighted Average Coupon (as a percent)																											6.10%	6.20%														7.90%	9.80%							10.80%	10.30%										3.50%	5.30%	4.70%	4.70%
Weighted Average Life																											4 years 3 months 18 days	3 years 9 months 18 days														3 years 6 months	4 years							3 years 6 months	3 years 7 months 6 days										4 years 10 months 24 days	9 years 3 months 18 days	2 years 4 months 24 days	3 years 2 months 12 days
Loans with variable rates of interest (as a percent)	64.10%
Variable rate basis of loans	LIBOR or EURIBOR							three-month EURIBOR
Weighted average spread of loans (as a percent)	6.17%			0.52%				0.70%
Effective variable rate basis (as a percent)				0.1789%	0.2087%	0.19%	0.30%		0.225%			0.19%	0.50%	3.00%	2.00%
Allowance for loan losses as a percent of carrying amount	6.30%	3.70%																		1.50%		5.00%
Amount of loan impairment charges on individual loans held for investment	0	0
Mortgage funded at closing																											225,000,000			50,600,000																																									98,900,000	122,900,000	115,000,000	112,000,000	115,000,000				53,800,000
Number of luxury condominium residences to be developed from loan acquired or originated																														30
Numbers of loans																																																																					8	2
Movement of loans held for investment
Balance at the beginning of the period	3,000,335,000
Acquisitions/Origination	2,506,378,000		264,517,000
Capitalized Interest	12,481,000
Basis of loans sold	(1,221,396,000)
Loan maturities	(329,636,000)
Principal repayments	(65,272,000)
Discount accretion/premium amortization	26,917,000
Changes in fair value	26,315,000
Unrealized foreign currency remeasurement gain	3,784,000
Capitalized cost written off	1,517,000
Loan loss allowance	(1,915,000)
Balance at the end of the period	4,220,991,000	3,000,335,000
Number of new loans																													74
Number of Class A office buildings with loans																																																																										8
Number of retail properties																																																																														20		225
Future funding																																																																														24,600,000	12,900,000
Number of stories within a building collateralizing loans originated or acquired																																																																										2
Carrying value of loans sold into a securitization an independent third party																																																																													100,000,000
Proceeds from sale of mortgage loan																																																																													99,400,000
Area of land (in square feet)																															844,820
Number of properties collateralizing loans originated or acquired																																15	2,509
Change in reserve for loan losses
Reserve for loan losses at beginning of year	2,061,000
Provision for loan losses	1,915,000
Reserve for loan losses at end of period	3,976,000	2,061,000
Recorded investment in loans related to the allowance for loan loss	$ 265,068,000