Debt and Preferred Equity Investments (Details) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended																				1 Months Ended							1 Months Ended									1 Months Ended																													1 Months Ended	9 Months Ended						1 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Dec. 31, 2011	Sep. 30, 2013 Debt investment		Dec. 31, 2012 Debt investment		Sep. 30, 2013 Fixed rate debt	Dec. 31, 2012 Fixed rate debt	Sep. 30, 2013 Other loan with an initial maturity of March 2015	Dec. 31, 2012 Other loan with an initial maturity of March 2015	Sep. 30, 2013 Mezzanine loan with an initial maturity date of February 2016	Dec. 31, 2012 Mezzanine loan with an initial maturity date of February 2016	Sep. 30, 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	Sep. 30, 2013 Mezzanine loan with an initial maturity date of May 2016	Dec. 31, 2012 Mezzanine loan with an initial maturity date of May 2016	Sep. 30, 2013 Junior participation with an initial maturity date of June 2016	Dec. 31, 2012 Junior participation with an initial maturity date of June 2016	Sep. 30, 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. 31, 2013 Mortgage/Mezzanine loan with an initial maturity date of March 2017	Sep. 30, 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		Sep. 30, 2013 Other loan with an initial maturity of September 2021	Dec. 31, 2012 Other loan with an initial maturity of September 2021	May 31, 2013 Mortgage	Sep. 30, 2013 Mortgage		Dec. 31, 2012 Mortgage		Sep. 30, 2013 Total floating rate	Dec. 31, 2012 Total floating rate	Sep. 30, 2013 Mezzanine loan with an initial maturity date of December 2013	Dec. 31, 2012 Mezzanine loan with an initial maturity date of December 2013	Jun. 30, 2013 Junior participation with an initial maturity date of June 2013 extended to February 2014	Sep. 30, 2013 Junior participation with an initial maturity date of June 2013 extended to February 2014		Dec. 31, 2012 Junior participation with an initial maturity date of June 2013 extended to February 2014		Sep. 30, 2013 Junior participation with an initial maturity date of February 2014		Dec. 31, 2012 Junior participation with an initial maturity date of February 2014		Sep. 30, 2013 Mortgage/Mezzanine Loan with an initial maturity date of July 2014	Dec. 31, 2012 Mortgage/Mezzanine Loan with an initial maturity date of July 2014	Sep. 30, 2013 Mezzanine loan with an initial maturity date of July 2014		Dec. 31, 2012 Mezzanine loan with an initial maturity date of July 2014		Sep. 30, 2013 Mezzanine loan with an initial maturity date of August 2014	Dec. 31, 2012 Mezzanine loan with an initial maturity date of August 2014	Sep. 30, 2013 Mortgage with initial maturity date of September 2014	Dec. 31, 2012 Mortgage with initial maturity date of September 2014	Sep. 30, 2013 Mezzanine Loan with initial maturity date of October 2014		Dec. 31, 2012 Mezzanine Loan with initial maturity date of October 2014		Sep. 30, 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		Sep. 30, 2013 Mezzainine Loan with an Initial Maturity Date of September 2015 [Member]	Dec. 31, 2012 Mezzainine Loan with an Initial Maturity Date of September 2015 [Member]	Jun. 30, 2013 Mezzanine loan with an initial maturity date of December 2015	Sep. 30, 2013 Mezzanine loan with an initial maturity date of December 2015		Dec. 31, 2012 Mezzanine loan with an initial maturity date of December 2015		Sep. 30, 2013 Mortgage with initial maturity date of March 2016	Dec. 31, 2012 Mortgage with initial maturity date of March 2016	Jun. 30, 2013 Mezzanine loan with an initial maturity date of June 2016	Sep. 30, 2013 Mezzanine loan with an initial maturity date of June 2016		Dec. 31, 2012 Mezzanine loan with an initial maturity date of June 2016		Sep. 30, 2013 Mezzanine loan with an initial maturity date of July 2016	Dec. 31, 2012 Mezzanine loan with an initial maturity date of July 2016	Sep. 30, 2013 Mortgage/Mezzanine Loan with an initial maturity date of July 2018	Dec. 31, 2012 Mortgage/Mezzanine Loan with an initial maturity date of July 2018	Sep. 30, 2013 Other Liabilities [Member] Mezzanine loan with an initial maturity date of July 2014
Debt investment
Increase in debt and preferred equity investments (net of discounts and deferred origination fees), including investments classified as held-for-sale			$ 497,400,000	$ 374,000,000
Decrease in debt and preferred equity investments (net of discounts), including investments classified as held-for-sale			530,200,000	288,300,000
Loan loss reserves	0	0	0	3,000,000	3,000,000
Aggregate weighted average current yield (as a percent)			11.30%
Senior Financing	4,465,422,000		4,465,422,000								2,369,855,000		398,500,000		205,000,000		167,355,000		177,000,000		133,000,000		165,000,000			1,109,000,000	[1]			15,000,000			0	[2]			2,095,567,000		0			57,750,000	[3]			80,932,000	[4]			330,000,000		62,500,000	[5]			180,000,000		0		87,374,000	[6]			0	[7]			110,000,000			92,711,000	[8]			775,000,000			160,000,000	[9]			87,300,000		72,000,000
Carrying Value, Net of Discounts and Deferred Origination Fees, at fixed rate											344,374,000	583,565,000	14,837,000	0	67,740,000	66,307,000	44,549,000	44,013,000	15,226,000	15,906,000	49,000,000	49,000,000	71,254,000	70,967,000		78,268,000	[1]	115,804,000	[1]	3,500,000	3,500,000		0	[2]	218,068,000	[2]
Carrying Value, Net of Discounts and Deferred Origination Fees, at floating rate																																					617,054,000	433,290,000	29,912,000	0		10,869,000	[3]	10,869,000	[3]	23,953,000	[4]	0	[4]	131,595,000	131,231,000	37,394,000	[5]	37,288,000	[5]	59,852,000	59,739,000	14,855,000	14,745,000	37,365,000	[6]	34,444,000	[6]	53,258,000	[7]	47,253,000	[7]	48,991,000	0		27,772,000	[8]	55,336,000	[8]	72,585,000	0		22,515,000	[9]	7,624,000	[9]	25,580,000	34,761,000	20,558,000	0
Carrying value, net of discounts							961,428,000		1,016,855,000
Loan loss reserve	(4,000,000)		(4,000,000)		(7,000,000)	(50,175,000)	(4,000,000)	[10]	(7,000,000)	[10]
Total, net of reserve							957,428,000		1,009,855,000
Percentage of loan sold (percent)																									50.00%																																													50.00%
Amount recovered from sale of loan																									57,800,000
Additional income recognized on sale																									12,900,000							6,400,000
Value of mortgage																																																																						85,000,000							30,000,000
Extension term (extension term)																																									4 months
Additional commitments to fund in connection with loan																																														900,000														12,300,000				5,200,000							13,600,000
Loan Participation Amount included in Other assets and/or Other liabilities																																																																													7,400,000									5,000,000	[5]
Amount funded in origination																																																																							56,300,000
Repayments of debt																																																																													$ 15,000,000

[1] Interest is added to the principal balance for this accrual only loan. In January 2013, we sold 50% of the mezzanine loan for $57.8 million and recognized additional income of $12.9 million, which is included in investment and preferred equity income on the consolidated statements of income. The unaccrued interest during the period in which the loan was on non-accrual status is being accreted as of January 2013.

[2] In connection with the repayment of the loan in May 2013, we recognized additional income of $6.4 million, which is included in investment and preferred equity income on our consolidated statements of income.

[3] In June 2013, the loan was extended to February 2014, subject to an additional four-month extension option.

[4] As of September 30, 2013, we were committed to fund an additional $0.9 million in connection with this loan.

[5] As a result of the transfer not meeting the conditions for sale accounting, the $5.0 million portion of the outstanding loan that was participated out has been recorded in other liabilities in the accompanying consolidated balance sheets.

[6] As of September 30, 2013, we were committed to fund an additional $12.3 million in connection with this loan.

[7] As of September 30, 2013, we were committed to fund an additional $5.2 million in connection with this loan.

[8] We funded $56.3 million at origination. In June 2013, we sold 50% of our interest in the $85.0 million mezzanine loan. As of September 30, 2013, we were committed to fund an additional $13.6 million in connection with our share of this loan.

[9] As part of the refinancing of the related senior mortgage in June 2013, we originated a $30.0 million mezzanine loan and our previous investment in the amount of $15.0 million, including the $7.4 million participated interest, was repaid in full. Following the refinancing, we entered into a loan participation agreement in the amount of $7.4 million on this $30.0 million mezzanine loan. Due to our continued involvement with the loan, the portion that was participated out has been recorded in other assets and other liabilities in the accompanying consolidated balance sheets.

[10] Loan loss reserves are specifically allocated to investments. Our reserves reflect management's judgment of the probability and severity of losses based on Level 3 data. We cannot be certain that our judgment will prove to be correct or that reserves will be adequate over time to protect against potential future losses.