Debt and Preferred Equity Investments (Details) (USD $)	3 Months Ended																			0 Months Ended												1 Months Ended			3 Months Ended		1 Months Ended				1 Months Ended											1 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Dec. 31, 2011	Mar. 31, 2013 Debt investment	Dec. 31, 2012 Debt investment	Mar. 31, 2013 Total fixed rate	Dec. 31, 2012 Total fixed rate	Mar. 31, 2013 Other loan with an initial maturity date of March 2015	Mar. 31, 2013 Mezzanine loan with an initial maturity date of February 2016	Dec. 31, 2012 Mezzanine loan with an initial maturity date of February 2016	Mar. 31, 2013 Mortgage/Mezzanine loan with an initial maturity date of May 2016	Dec. 31, 2012 Mortgage/Mezzanine loan with an initial maturity date of May 2016	Mar. 31, 2013 Mezzanine loan with an initial maturity date of May 2016	Dec. 31, 2012 Mezzanine loan with an initial maturity date of May 2016	Mar. 31, 2013 Junior participation with an initial maturity date of June 2016	Dec. 31, 2012 Junior participation with an initial maturity date of June 2016	Mar. 31, 2013 Mezzanine loan with an initial maturity date of November 2016	Dec. 31, 2012 Mezzanine loan with an initial maturity date of November 2016	Jan. 13, 2013 Mortgage/Mezzanine Loan With An Initial Maturity Date Of March 2017	Mar. 31, 2013 Mortgage/Mezzanine Loan With An Initial Maturity Date Of March 2017	Dec. 31, 2012 Mortgage/Mezzanine Loan With An Initial Maturity Date Of March 2017	Mar. 31, 2013 Other loan with an initial maturity date of September 2021	Dec. 31, 2012 Other loan with an initial maturity date of September 2021	Mar. 31, 2013 Mortgage	Dec. 31, 2012 Mortgage	Nov. 30, 2012 Mortgage	Mar. 31, 2013 Total floating rate	Dec. 31, 2012 Total floating rate	Mar. 31, 2013 Junior participation with an initial maturity date of June 2013	Dec. 31, 2012 Junior participation with an initial maturity date of June 2013	Nov. 30, 2011 Mezzanine loan with an initial maturity date of July 2013	Mar. 31, 2013 Mezzanine loan with an initial maturity date of July 2013	Dec. 31, 2012 Mezzanine loan with an initial maturity date of July 2013	Mar. 31, 2013 Mezzanine loan with an initial maturity date of December 2013 item	Feb. 28, 2013 Mezzanine loan with an initial maturity date of December 2013	Sep. 30, 2012 Mortgage/Mezzanine Loan with initial maturity date of July 2014	Jul. 31, 2012 Mortgage/Mezzanine Loan with initial maturity date of July 2014	Mar. 31, 2013 Mortgage/Mezzanine Loan with initial maturity date of July 2014	Dec. 31, 2012 Mortgage/Mezzanine Loan with initial maturity date of July 2014	Nov. 30, 2012 Mezzanine loan with an initial maturity date of July 2014	Mar. 31, 2013 Mezzanine loan with an initial maturity date of July 2014	Dec. 31, 2012 Mezzanine loan with an initial maturity date of July 2014	Mar. 31, 2013 Mezzanine loan with an initial maturity date of August 2014	Dec. 31, 2012 Mezzanine loan with an initial maturity date of August 2014	Mar. 31, 2013 Mortgage with initial maturity date of September 2014	Dec. 31, 2012 Mortgage with initial maturity date of September 2014	Mar. 31, 2013 Mortgage/Mezzanine loan with an initial maturity date of February 2015	Dec. 31, 2012 Mortgage/Mezzanine loan with an initial maturity date of February 2015	Mar. 31, 2013 Mezzanine Loan with initial maturity date of December 2015	Dec. 31, 2012 Mezzanine Loan with initial maturity date of December 2015	Mar. 31, 2013 Mezzanine loan with an initial maturity date of March 2016	Mar. 31, 2013 Mezzanine loan with an initial maturity date of July 2016	Dec. 31, 2012 Mezzanine loan with an initial maturity date of July 2016	Mar. 31, 2013 Mezzanine loan with an initial maturity date of October 2016	Dec. 31, 2012 Mezzanine loan with an initial maturity date of October 2016
Debt and Preferred Equity Investments
Increase in debt and preferred equity investments (net of discounts), including investments classified as held-for-sale	$ 208,600,000	$ 76,300,000
Decrease in debt and preferred equity investments (net of discounts), including investments classified as held-for-sale	121,900,000	59,700,000
Loan loss reserves recorded	0	3,000,000
Gain (loss) on sale of property	1,113,000	6,627,000
Debt investment
Aggregate weighted average current yield (as a percent)	11.10%
Senior Financing	4,073,528,000						2,372,067,000		399,500,000	205,000,000		168,567,000		177,000,000		133,000,000		165,000,000			1,109,000,000		15,000,000					1,701,461,000		60,250,000			75,000,000						330,000,000			62,500,000		170,000,000						92,711,000		775,000,000	55,000,000		81,000,000
Carrying Value, Net of Discounts					1,104,227,000	1,023,318,000	559,272,000	586,385,000	15,000,000	66,936,000	66,544,000	46,511,000	46,496,000	15,644,000	15,906,000	49,000,000	49,000,000	71,119,000	71,067,000		73,292,000	115,804,000	3,500,000	3,500,000	218,270,000	218,068,000		544,955,000	436,933,000	10,875,000	10,875,000		7,650,000	7,650,000	30,000,000			182,000,000	132,000,000	132,000,000		37,500,000	37,500,000	60,000,000	60,000,000	15,000,000	15,000,000	50,439,000	47,679,000	56,289,000	56,289,000	75,000,000	35,000,000	35,000,000	35,202,000	34,940,000
Loan loss reserve	(7,000,000)		(7,000,000)	(50,175,000)	(7,000,000)	(7,000,000)
Carrying value after deduction of loan loss reserves	1,443,834,000		1,357,203,000		1,097,227,000	1,016,318,000
Percentage of loan sold																				50.00%																																50.00%
Acquisition of non-performing loan																											219,000,000
Loan participation amount included in other assets and other liabilities																																7,400,000									5,000,000
Value of mortgage																																15,000,000						462,000,000
Mortgage loans																																				100,000,000
Number of extension options																																			2
Extension option available for debt instrument																																			1 year
Amount recovered from sale of loan																				57,800,000
Additional income on sale of loan																				12,900,000
Proceeds from collection of loans receivable																																						49,900,000
Interest in senior mortgage sold																																					50,000,000
Additional commitments to fund in connection with loan																																																8,300,000		28,700,000					14,800,000
Loan originated																																																				$ 150,000,000