Debt and Preferred Equity Investments (Details) (USD $)	12 Months Ended					3 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012	Mar. 31, 2014	Dec. 31, 2011	Sep. 30, 2014
Debt investment
Increase in debt and preferred equity investments (net of discounts), including investments classified as held-for-sale	$ 680,100,000		$ 601,300,000
Decrease in debt and preferred equity investments (net of discounts), including investments classified as held-for-sale	576,100,000		644,900,000
Aggregate weighted average current yield (as a percent)	10.33%
Debt Investments Held [Abstract]
Carrying Value, Net of Discounts and Deferred Origination Fees	1,408,804,000		1,304,839,000
Loan loss reserve	0		(1,000,000)		(7,000,000)		(50,175,000)
Origination of debt and preferred equity investments	617,090,000		555,137,000		645,229,000
Debt investment
Debt Investments Held [Abstract]
Future Funding Obligations	48,127,000
Senior Financing	5,693,315,000
Carrying Value, Net of Discounts and Deferred Origination Fees	1,275,809,000	[1]	936,475,000	[1]
Loan loss reserve	0	[1]	(1,000,000)	[1]
Total, net of reserve	1,275,809,000	[1]	935,475,000	[1]
Total fixed rate
Debt Investments Held [Abstract]
Future Funding Obligations	16,424,000
Senior Financing	3,448,250,000
Carrying Value, Net of Discounts and Deferred Origination Fees	582,174,000	[1]	385,604,000	[1]
Total fixed rate | Junior Mortgage Participation, March 2015
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	398,500,000
Carrying Value, Net of Discounts and Deferred Origination Fees	11,934,000	[1]	11,856,000	[1]
Total fixed rate | Junior Mortgage Participation/Mezzanine Loan, February 2016
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	205,000,000
Carrying Value, Net of Discounts and Deferred Origination Fees	70,688,000	[1]	68,319,000	[1]
Total fixed rate | Other, Various
Debt Investments Held [Abstract]
Future Funding Obligations	0	[2]
Senior Financing	0	[2]
Carrying Value, Net of Discounts and Deferred Origination Fees	45,611,000	[1],[2]	44,742,000	[1],[2]
Total fixed rate | Mezzanine Loan, May 2016
Debt Investments Held [Abstract]
Future Funding Obligations	0	[3]
Senior Financing	177,000,000	[3]
Carrying Value, Net of Discounts and Deferred Origination Fees	14,068,000	[1],[3]	15,012,000	[1],[3]
Total fixed rate | Junior Mortgage Participation, June 2016
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	133,000,000
Carrying Value, Net of Discounts and Deferred Origination Fees	49,000,000	[1]	49,000,000	[1]
Total fixed rate | Junior Mortgage Participation/Mezzanine Loan, March 2017
Debt Investments Held [Abstract]
Future Funding Obligations	0	[4]
Senior Financing	1,109,000,000	[4]
Carrying Value, Net of Discounts and Deferred Origination Fees	98,934,000	[1],[4]	26,884,000	[1],[4]
Carrying Value, Net of Discounts and Deferred Origination Fees	30,000,000
Carrying amount of Notes defeased	66,700,000
Interest income recognized previously accrued						10,100,000
Origination of debt and preferred equity investments	67,300,000
Total fixed rate | Other, March 2017
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value, Net of Discounts and Deferred Origination Fees	65,770,000	[1]	54,099,000	[1]
Total fixed rate | Mezzanine Loan, June 2017
Debt Investments Held [Abstract]
Future Funding Obligations	16,424,000	[5]
Senior Financing	521,750,000	[5]
Carrying Value, Net of Discounts and Deferred Origination Fees	24,608,000	[1],[5]	20,954,000	[1],[5]
Amount participated out	41,300,000
Total fixed rate | Mezzanine Loan, July 2018
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	539,000,000
Carrying Value, Net of Discounts and Deferred Origination Fees	49,629,000	[1]	0	[1]
Total fixed rate | Mortgage Loan, February 2019
Debt Investments Held [Abstract]
Future Funding Obligations	0	[6]
Senior Financing	0	[6]
Carrying Value, Net of Discounts and Deferred Origination Fees	26,209,000	[1],[6]	0	[1],[6]
Loan acquired								26,400,000
Discount amount								200,000
Total fixed rate | Mortgage Loan, August 2019
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value, Net of Discounts and Deferred Origination Fees	637,000	[1]	0	[1]
Total fixed rate | Mezzanine Loan, September 2021
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	15,000,000
Carrying Value, Net of Discounts and Deferred Origination Fees	3,500,000	[1]	3,500,000	[1]
Total fixed rate | Mezzanine Loan, November 2023
Debt Investments Held [Abstract]
Future Funding Obligations	0	[7]
Senior Financing	90,000,000	[7]
Carrying Value, Net of Discounts and Deferred Origination Fees	19,930,000	[1],[7]	19,926,000	[1],[7]
Amount participated out	5,000,000
Total fixed rate | Mezzanine Loan, January 2025
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	95,000,000
Carrying Value, Net of Discounts and Deferred Origination Fees	30,000,000	[1]	0	[1]
Total fixed rate | Mezzanine Loan, November 2016
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	165,000,000
Carrying Value, Net of Discounts and Deferred Origination Fees	71,656,000	[1]	71,312,000	[1]
Total fixed rate | Other Various, Junior Participation Loan
Debt Investments Held [Abstract]
Carrying amount of Notes defeased	22,600,000
Total fixed rate | Other Various, Mezzanine Loan
Debt Investments Held [Abstract]
Carrying amount of Notes defeased	23,000,000
Total fixed rate | Junior Mortgage Participation, Related To Mortgage Loan, February 2019
Debt Investments Held [Abstract]
Loan acquired								5,700,000
Discount amount								5,700,000
Total floating rate
Debt Investments Held [Abstract]
Future Funding Obligations	31,703,000
Senior Financing	2,245,065,000
Carrying Value, Net of Discounts and Deferred Origination Fees	693,635,000	[1]	550,871,000	[1]
Total floating rate | Mezzanine Loan, April 2015
Debt Investments Held [Abstract]
Future Funding Obligations	7,785,000
Senior Financing	50,000,000
Carrying Value, Net of Discounts and Deferred Origination Fees	37,322,000	[1]	0	[1]
Total floating rate | Mortgage Mezzanine Loan, June 2015
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value, Net of Discounts and Deferred Origination Fees	109,527,000	[1]	0	[1]
Total floating rate | Mezzanine Loan, September 2015
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	110,000,000
Carrying Value, Net of Discounts and Deferred Origination Fees	49,614,000	[1]	49,110,000	[1]
Total floating rate | Mezzanine Loan, December 2015
Debt Investments Held [Abstract]
Future Funding Obligations	7,249,000
Senior Financing	113,633,000
Carrying Value, Net of Discounts and Deferred Origination Fees	42,750,000	[1]	27,662,000	[1]
Total floating rate | Mezzanine Loan, March 2016
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	775,000,000
Carrying Value, Net of Discounts and Deferred Origination Fees	73,402,000	[1]	72,823,000	[1]
Total floating rate | Mezzanine Loan, June 2016
Debt Investments Held [Abstract]
Future Funding Obligations	0	[8]
Senior Financing	160,000,000	[8]
Carrying Value, Net of Discounts and Deferred Origination Fees	22,573,000	[1],[8]	22,526,000	[1],[8]
Amount participated out	7,400,000
Total floating rate | Mezzanine Loan, July 2016
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	115,000,000
Carrying Value, Net of Discounts and Deferred Origination Fees	24,910,000	[1]	25,590,000	[1]
Total floating rate | Mezzanine Loan, November 2016
Debt Investments Held [Abstract]
Future Funding Obligations	3,641,000
Senior Financing	172,105,000
Carrying Value, Net of Discounts and Deferred Origination Fees	33,726,000	[1]	25,725,000	[1]
Total floating rate | Mezzanine Loan, November 2016
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	360,000,000
Carrying Value, Net of Discounts and Deferred Origination Fees	99,023,000	[1]	0	[1]
Total floating rate | Mezzanine Loan, December 2016
Debt Investments Held [Abstract]
Future Funding Obligations	333,000
Senior Financing	33,833,000
Carrying Value, Net of Discounts and Deferred Origination Fees	11,835,000	[1]	11,798,000	[1]
Total floating rate | Mezzanine Loan, January 2017
Debt Investments Held [Abstract]
Future Funding Obligations	9,053,000
Senior Financing	91,727,000
Carrying Value, Net of Discounts and Deferred Origination Fees	20,651,000	[1]	0	[1]
Total floating rate | Mortgage/Mezzanine Loan, July 2017
Debt Investments Held [Abstract]
Future Funding Obligations	2,847,000
Senior Financing	110,767,000
Carrying Value, Net of Discounts and Deferred Origination Fees	38,524,000	[1]	0	[1]
Total floating rate | Mortgage/Mezzanine Loan, July 2017
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value, Net of Discounts and Deferred Origination Fees	22,803,000	[1]	0	[1]
Total floating rate | Mortgage/Mezzanine Loan, September 2017
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value, Net of Discounts and Deferred Origination Fees	16,848,000	[1]	0	[1]
Total floating rate | Mezzanine Loan, November 2017
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	60,000,000
Carrying Value, Net of Discounts and Deferred Origination Fees	14,859,000	[1]	0	[1]
Total floating rate | Mortgage Mezzanine Loan, December 2017
Debt Investments Held [Abstract]
Future Funding Obligations	795,000	[9]
Senior Financing	0	[9]
Carrying Value, Net of Discounts and Deferred Origination Fees	14,845,000	[1],[9]	0	[1],[9]
Amount participated out	5,100,000
Total floating rate | Junior Mortgage Participation/Mezzanine Loan, July 2018
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	55,000,000
Carrying Value, Net of Discounts and Deferred Origination Fees	20,533,000	[1]	20,553,000	[1]
Total floating rate | Mortgage Mezzanine Loan, February 2019
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value, Net of Discounts and Deferred Origination Fees	18,083,000	[1]	0	[1]
Total floating rate | Mezzanine Loan, March 2019
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	38,000,000
Carrying Value, Net of Discounts and Deferred Origination Fees	21,807,000	[1]	0	[1]
Total floating rate | Mortgage Loan, Repaid in May 2014
Debt Investments Held [Abstract]
Future Funding Obligations	0	[10]
Senior Financing	0	[10]
Carrying Value, Net of Discounts and Deferred Origination Fees	0	[1],[10]	30,000,000	[1],[10]
Total floating rate | Junior Mortgage Participation, Repaid In July 2014
Debt Investments Held [Abstract]
Future Funding Obligations	0	[11]
Senior Financing	0	[11]
Carrying Value, Net of Discounts and Deferred Origination Fees	0	[1],[11]	24,046,000	[1],[11]
Total floating rate | Junior Mortgage Participation/Mezzanine Loan, Repaid In July 2014
Debt Investments Held [Abstract]
Future Funding Obligations	0	[11]
Senior Financing	0	[11]
Carrying Value, Net of Discounts and Deferred Origination Fees	0	[1],[11]	131,724,000	[1],[11]
Total floating rate | Mezzanine Loan, Repaid in August 2014
Debt Investments Held [Abstract]
Future Funding Obligations	0	[12]
Senior Financing	0	[12]
Carrying Value, Net of Discounts and Deferred Origination Fees	0	[1],[12]	59,892,000	[1],[12]
Total floating rate | Junior Mortgage Participation, Repaid In August 2014
Debt Investments Held [Abstract]
Future Funding Obligations	0	[12]
Senior Financing	0	[12]
Carrying Value, Net of Discounts and Deferred Origination Fees	0	[1],[12]	10,873,000	[1],[12]
Total floating rate | Mezzanine Loan, Repaid In August 2014
Debt Investments Held [Abstract]
Future Funding Obligations	0	[12]
Senior Financing	0	[12]
Carrying Value, Net of Discounts and Deferred Origination Fees	$ 0	[1],[12]	$ 38,549,000	[1],[12]

[1] Carrying value is net of discounts, premiums, original issue discounts and deferred origination fees.

[2] During the fourth quarter of 2014, both our $22.6 million junior participation and our $23.0 mezzanine loan were defeased and are now collateralized by defeasance securities. In connection with the defeasance, the maturity date of the mortgage in which we are a junior participant was accelerated from the May 2016 to February 2016, per the terms of the loan agreement. The maturity date of the mezzanine loan was not changed in connection with the defeasance and will mature in May 2016.

[3] This loan was repaid in February 2015.

[4] During the first quarter of 2014, we recognized $10.1 million of previously unaccrued interest income which was deemed collectible as a result of the sale of the underlying property, which closed in June 2014. In connection with the sale of the underlying property, our existing $66.7 million mezzanine loan was defeased and is now shown separately, as it is collateralized by defeasance securities. The buyer assumed our $30.0 million participating interest in the mortgage and we acquired a $67.3 million participating interest in the new mezzanine loan.

[5] Carrying value is net of $41.3 million that was participated out, which is included in other assets and other liabilities on the consolidated balance sheets as a result of the transfer not meeting the conditions for sale accounting.

[6] In September 2014, we acquired a $26.4 million mortgage loan at a $0.2 million discount and a $5.7 million junior mortgage participation at a $5.7 million discount. The junior mortgage participation was a nonperforming loan at acquisition and is currently on non-accrual status.

[7] Carrying value is net of $5.0 million that was participated out, which is included in other assets and other liabilities on the consolidated balance sheets as a result of the transfer not meeting the conditions for sale accounting.

[8] Carrying value is net of $7.4 million that was participated out, which is included in other assets and other liabilities on the consolidated balance sheets as a result of the transfer not meeting the conditions for sale accounting.

[9] Carrying value is net of $5.1 million that was participated out, which is included in other assets and other liabilities on the consolidated balance sheets as a result of the transfer not meeting the conditions for sale accounting.

[10] This loan was repaid in May 2014.

[11] This loan was repaid in July 2014.

[12] This loan was repaid in August 2014.