Debt and Preferred Equity Investments (Details)	3 Months Ended		12 Months Ended											0 Months Ended	1 Months Ended											1 Months Ended		1 Months Ended		1 Months Ended																				9 Months Ended					1 Months Ended			1 Months Ended			1 Months Ended
	Mar. 31, 2012 USD ($)	Jun. 30, 2011 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)	Dec. 31, 2009 USD ($)	Dec. 31, 2012 Debt investment USD ($)	Dec. 31, 2011 Debt investment USD ($)	Dec. 31, 2012 Total fixed rate USD ($)	Dec. 31, 2012 Other loan with an initial maturity of September 2021 USD ($)	Dec. 31, 2011 Other loan with an initial maturity of September 2021 USD ($)	Dec. 31, 2012 Mortgage/Mezzanine loan with an initial maturity date of March 2017 USD ($)	Dec. 31, 2011 Mortgage/Mezzanine loan with an initial maturity date of March 2017 USD ($)	Jan. 13, 2013 Mortgage/Mezzanine loan with an initial maturity date of March 2017 Subsequent event	Jan. 31, 2013 Mortgage/Mezzanine loan with an initial maturity date of March 2017 Subsequent event	Dec. 31, 2012 Mezzanine loan with an initial maturity date of November 2016 USD ($)	Dec. 31, 2011 Mezzanine loan with an initial maturity date of November 2016 USD ($)	Dec. 31, 2012 Junior participation with an initial maturity date of June 2016 USD ($)	Dec. 31, 2011 Junior participation with an initial maturity date of June 2016 USD ($)	Dec. 31, 2012 Mortgage/Mezzanine loan with an initial maturity date of May 2016 USD ($)	Dec. 31, 2011 Mortgage/Mezzanine loan with an initial maturity date of May 2016 USD ($)	Dec. 31, 2012 Mezzanine loan with an initial maturity date of May 2016 USD ($)	Dec. 31, 2011 Mezzanine loan with an initial maturity date of May 2016 USD ($)	Dec. 31, 2012 Mezzanine loan with an initial maturity date of February 2016 USD ($)	Dec. 31, 2011 Mezzanine loan with an initial maturity date of February 2016 USD ($)	Nov. 30, 2012 Mortgage USD ($)	Dec. 31, 2012 Mortgage USD ($)	Feb. 29, 2012 Junior Participation USD ($)	Dec. 31, 2011 Junior Participation USD ($)	Mar. 31, 2012 Junior Participation USD ($)	Dec. 31, 2011 Junior Participation USD ($)	Dec. 31, 2012 Mezzanine Loan with initial maturity date of October 2016 USD ($)	Dec. 31, 2011 Mezzanine Loan with initial maturity date of October 2016 USD ($)	Dec. 31, 2012 Mezzanine loan with an initial maturity date of July 2016 USD ($)	Dec. 31, 2011 Mezzanine loan with an initial maturity date of July 2016 USD ($)	Dec. 31, 2012 Mezzanine loan with an initial maturity date of December 2015 USD ($)	Dec. 31, 2012 Mortgage/Mezzanine loan with an initial maturity date of February 2015 USD ($)	Dec. 31, 2012 Mezzanine loan with an initial maturity date of August 2014 USD ($)	Dec. 31, 2011 Mezzanine loan with an initial maturity date of August 2014 USD ($)	Dec. 31, 2012 Mezzanine loan with an initial maturity date of July 2014 USD ($)	Nov. 30, 2012 Mezzanine loan with an initial maturity date of July 2014 USD ($)	Dec. 31, 2012 Mezzanine loan with an initial maturity date of July 2013 USD ($)	Dec. 31, 2011 Mezzanine loan with an initial maturity date of July 2013 USD ($)	Nov. 30, 2011 Mezzanine loan with an initial maturity date of July 2013 USD ($)	Dec. 31, 2012 Junior participation with an initial maturity date of June 2013 USD ($)	Dec. 31, 2011 Junior participation with an initial maturity date of June 2013 USD ($)	Dec. 31, 2011 Mezzanine loan USD ($)	Dec. 31, 2012 Total floating rate USD ($)	Dec. 31, 2012 Mortgage with initial maturity date of September 2014 USD ($)	Sep. 30, 2012 Mortgage/Mezzanine Loan with an initial maturity date of July 2014 USD ($)	Dec. 31, 2012 Mortgage/Mezzanine Loan with an initial maturity date of July 2014 USD ($)	Jul. 31, 2012 Mortgage/Mezzanine Loan with an initial maturity date of July 2014 USD ($)	Dec. 31, 2011 Mortgage/Mezzanine Loan with an initial maturity date of July 2014 USD ($)	Nov. 30, 2011 Mortgage/Mezzanine Loan with an initial maturity date of July 2014	Jun. 30, 2011 Mortgage with an initial maturity date of February 2013 USD ($)	Dec. 31, 2011 Mortgage with an initial maturity date of February 2013 USD ($)	Sep. 30, 2011 Mortgage with an initial maturity date of February 2013 USD ($)	Jun. 30, 2012 Mezzanine loan with an initial maturity, current period	Sep. 28, 2012 Mezzanine loan with an initial maturity, current period	Dec. 31, 2011 Mezzanine loan with an initial maturity, current period USD ($)	Nov. 30, 2012 Mortgage with an initial maturity, current period USD ($)	Nov. 30, 2012 Mortgage with an initial maturity, current period GBP (£)	Dec. 31, 2012 Mortgage with an initial maturity, current period	Dec. 31, 2011 Mortgage with an initial maturity, current period USD ($)	Dec. 31, 2011 Other Loan USD ($)
Debt and Preferred Equity Investments
Increase in debt and preferred equity investments (net of discounts), including investments classified as held-for-sale			$ 672,900,000	$ 622,500,000
Decrease in debt and preferred equity investments (net of discounts), including investments classified as held-for-sale			298,700,000	589,400,000
Loan loss reserves recorded			3,000,000	10,900,000
Debt investment
Aggregate weighted average current yield (as a percent)			9.79%
Senior Financing			2,899,673,000						1,973,212,000	15,000,000		1,109,000,000				165,000,000		133,000,000		169,212,000		177,000,000		205,000,000								81,000,000		55,000,000		92,711,000		170,000,000		62,500,000		75,000,000			60,250,000			926,461,000			330,000,000
Carrying Value, Net of Discounts, at fixed rate							586,385,000	349,918,000		3,500,000	3,500,000	115,804,000	108,817,000			71,067,000	40,375,000	49,000,000	49,000,000	46,496,000	46,416,000	15,906,000	17,112,000	66,544,000	64,973,000		218,068,000		8,725,000		11,000,000																					49,900,000
Carrying Value, Net of Discounts, at floating rate			1,357,203,000	985,942,000			436,933,000	290,139,000																								34,940,000	34,940,000	35,000,000	35,000,000	56,289,000	47,679,000	60,000,000	60,000,000	37,500,000		7,650,000	7,650,000		10,875,000	10,875,000	10,000,000		15,000,000		132,000,000		30,747,000			3,000,000				8,392,000				86,339,000	3,196,000
Loan Participation Amount included in Other assets & Other liabilities																																									5,000,000			7,400,000								182,000,000					28,500,000
Carrying value, net of discounts							1,023,318,000	640,057,000
Loan loss reserve			(7,000,000)	(50,175,000)	(61,361,000)	(93,844,000)	(7,000,000)	(19,125,000)
Total, net of reserve							1,016,318,000	620,932,000
Percentage of loan sold														50.00%	50.00%
Consideration as percentage of accrued balance on sale of loan														97.00%
Loans acquired																										219,000,000
Amount recovered from sale of loan																												400,000		2,000,000
Ownership interest in consolidated joint venture holding the debt investment (as a percent)																																																															88.00%
Interest in property (as a percent)																																																						50.00%
Additional ownership interest acquired (as a percent)																																																											27.63%
Ownership interest in the joint venture hold by Blackstone																																																											56.30%
Additional funding provided																																																							5,500,000
Value of mortgage																																												15,000,000								462,000,000					31,500,000
Additional participation interest acquired (as a percent)																																																										38.60%
Additional commitments to fund in connection with loan																																15,100,000				28,700,000	11,000,000
Sale of interest on the senior mortgage loan																																																		50,000,000
Sale of entity that held property																																																													100,000,000	62,500,000
Gain on sale of property	$ 6,627,000	$ 46,085,000	$ 6,627,000	$ 46,085,000	$ 35,485,000																																																								$ 8,900,000