Loans Receivable (Details) (USD $) In Thousands, unless otherwise specified	0 Months Ended	1 Months Ended	12 Months Ended									12 Months Ended			12 Months Ended		12 Months Ended				12 Months Ended	1 Months Ended	12 Months Ended		1 Months Ended	12 Months Ended					12 Months Ended		12 Months Ended		12 Months Ended					12 Months Ended
	Aug. 06, 2012	Jan. 14, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 B Note [Member]	Dec. 31, 2011 B Note [Member]	Dec. 31, 2012 Mezzanine [Member]	Dec. 31, 2011 Mezzanine [Member]	Dec. 31, 2012 Whole Loan [Member]	Dec. 31, 2011 Whole Loan [Member]	Dec. 31, 2012 Corporate Loan [Member]	Dec. 31, 2012 Hotel Wales [Member] Whole Loan [Member]	Dec. 31, 2011 Hotel Wales [Member] Whole Loan [Member]	Dec. 31, 2012 Renaissance Walk [Member] Mezzanine [Member]	Dec. 31, 2011 Renaissance Walk [Member] Mezzanine [Member]	Dec. 31, 2012 Fenway Shea [Member] Whole Loan [Member]	Dec. 31, 2012 The Shops At Wailea [Member] B Note [Member]	Dec. 31, 2012 Legacy Orchard [Member] Corporate Loan [Member]	Dec. 31, 2011 Legacy Orchard [Member] Corporate Loan [Member]	Dec. 31, 2012 Queensridge [Member] Whole Loan [Member]	Jan. 14, 2011 San Marbeya [Member]	Dec. 31, 2012 San Marbeya [Member] Whole Loan [Member]	Dec. 31, 2011 San Marbeya [Member] Whole Loan [Member]	May 31, 2012 127 West 25th Street [Member]	Dec. 31, 2012 127 West 25th Street [Member] Mezzanine [Member]	Dec. 31, 2012 Churchill [Member] Whole Loan [Member]	Dec. 31, 2012 180 N. Michigan [Member] Mezzanine [Member]	Dec. 31, 2011 180 N. Michigan [Member] Mezzanine [Member]	Dec. 31, 2012 1515 Market [Member] Whole Loan [Member]	Dec. 31, 2012 Rockwell [Member] Mezzanine [Member]	Dec. 31, 2011 Rockwell [Member] Mezzanine [Member]	Dec. 31, 2012 500-512 7th Avenue [Member] B Note [Member]	Dec. 31, 2011 500-512 7th Avenue [Member] B Note [Member]	Dec. 31, 2012 Pinnacle II [Member] B Note [Member]	Dec. 31, 2012 Popiu Shopping Village [Member] B Note [Member]	Dec. 31, 2012 The Disney Building [Member] B Note [Member]	Dec. 31, 2012 Wellington Tower [Member] Mezzanine [Member]	Dec. 31, 2011 Wellington Tower [Member] Mezzanine [Member]	Dec. 31, 2012 Mentor Building [Member] Whole Loan [Member]	Dec. 31, 2011 160 Spear [Member] B Note [Member]	Dec. 31, 2011 160 Spear [Member] Mezzanine [Member]	Dec. 31, 2011 Magazine [Member] Mezzanine [Member]	Dec. 31, 2011 Marc- 29 East Madison [Member] Mezzanine [Member]
Accounts Notes And Loans Receivable [Line Items]
Mortgage Loans, Stated Interest Rate, Variable Rate Basis													LIBOR + 4.0%		LIBOR + 12.0%		0.12	0.0615	0.15		LIBOR + 11.5%		0.0588			0.14	LIBOR + 3.75%	0.0825			0.12		0.0719		0.0631	0.0662	0.059	0.0679		0.1
Summary of Trust's loans receivable
Interest rate on mortgage loans	9.00%	6.40%	3.95%									15.00%	4.00%		12.00%		12.00%	6.15%	15.00%		11.50%	4.85%	5.88%			14.00%	3.75%	8.25%			12.00%		71.90%		6.31%	6.62%	5.90%	6.79%		10.00%
Loans receivable, net			$ 211,250	$ 114,333	$ 110,395	$ 31,028	$ 21,534	$ 19,934	$ 36,447	$ 160,288	$ 56,352		$ 20,101	$ 20,101	$ 3,000	$ 3,000	$ 2,273	$ 5,376	$ 9,750	$ 9,750	$ 39,170		$ 27,149	$ 26,501		$ 8,687	$ 683	$ 5,237	$ 2,930	$ 58,650	$ 323	$ 275	$ 10,009	$ 9,979	$ 4,652	$ 1,948	$ 9,043	$ 2,687	$ 2,563	$ 2,512	$ 11,555	$ 4,846	$ 18,805	$ 4,028
Contractual maturity date												Oct. 31, 2014	Oct. 05, 2013		Jan. 01, 2014		Apr. 05, 2014	Oct. 06, 2014	Oct. 31, 2014		Nov. 15, 2014		Jan. 01, 2015		Apr. 30, 2015	Apr. 30, 2015	Jun. 01, 2015	Dec. 01, 2015			May 01, 2016		Jul. 11, 2016		Sep. 06, 2016	Jan. 06, 2017	Apr. 06, 2017	Jul. 11, 2017		Sep. 10, 2017