Debt and Preferred Equity Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Apr. 30, 2016	Sep. 30, 2014	Jul. 31, 2014
Debt investment
Increase in debt and preferred equity investments (net of discounts), including investments classified as held-for-sale	$ 1,015,000	$ 781,000
Decrease in debt and preferred equity investments (net of discounts), including investments classified as held-for-sale	$ 1,045,000	520,000
Mortgage Loans on Real Estate, Interest Rate	9.34%
Debt Investments Held [Abstract]
Carrying Value	$ 1,640,412	1,670,020
Mezzanine Loan, with an Initial Maturity Date of June 2017 [Member]
Debt Investments Held [Abstract]
Amount participated out	41,300
Mezzanine Loan, with an Initial Maturity Date of November 2023 [Member]
Debt Investments Held [Abstract]
Amount participated out	5,000
Mezzanine Loan with an Initial Maturity Date of June 2024 [Member]
Debt Investments Held [Abstract]
Amount participated out	12,000
Mezzanine Loan Repaid in April 2016 [Member]
Debt Investments Held [Abstract]
Carrying Value					$ 50,000
Equity Method Investment, Ownership Percentage			20.00%
Mortgage/Mezzanine Loan with an Initial Maturity Date of January 2017 [Member]
Debt Investments Held [Abstract]
Amount participated out	36,300
Mortgage/Mezzanine Loan with an Initial Maturity Date of June 2017 [Member]
Debt Investments Held [Abstract]
Amount participated out	14,500
Mezzanine Loan with an Initial Maturity Date of December 2017 [Member]
Debt Investments Held [Abstract]
Amount participated out	14,600
Mezzanine Loan with an Initial Maturity Date of December 2017, 2 [Member]
Debt Investments Held [Abstract]
Amount participated out	14,100
Mortgage Mezzanine Loan with an Initial Maturity Date of December 2017 [Member]
Debt Investments Held [Abstract]
Amount participated out	5,100
Debt investment
Debt Investments Held [Abstract]
Future Funding Obligations	270,465
Senior Financing	5,219,719
Carrying Value	1,592,537	1,627,844
Total fixed rate
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	2,264,566
Carrying Value	360,359	511,389
Total fixed rate | Junior Mortgage Participation or Mezzanine Loan with an Initial Maturity Date of March 2017 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	1,109,000
Carrying Value	193,422	104,661
Total fixed rate | Mezzanine Loan, with an Initial Maturity Date of June 2017 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	502,100
Carrying Value	66,129	41,115
Total fixed rate | Mortgage Loan With An Initial Maturity Date Of February 2019 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	26,311	26,262
Loan acquired				$ 26,400
Discount amount				200
Total fixed rate | Mortgage Loan with an Initial Maturity of August 2019 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	380	513
Total fixed rate | Mezzanine Loan with an Initial Maturity Date of September 2021 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	15,000
Carrying Value	3,500	3,500
Total fixed rate | Mezzanine Loan, with an Initial Maturity Date of November 2023 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	88,466
Carrying Value	12,692	19,936
Total fixed rate | Mezzanine Loan with an Initial Maturity Date of June 2024 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	115,000
Carrying Value	12,925	24,916
Total fixed rate | Mezzanine Loan, with an Initial Maturity Date of January 2025 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	95,000
Carrying Value	30,000	30,000
Total fixed rate | Mezzanine Loan with an Initial Maturity Date of November 2026 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	340,000
Carrying Value	15,000	0
Total fixed rate | Mezzanine Loan Repaid in July 2016 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0	72,102
Total fixed rate | Mezzanine Loan Repaid in April 2016 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0	49,691
Total fixed rate | Junior Mortgage Participation Loan Repaid in March 2016 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0	49,000
Total fixed rate | Loan Collateralized by Defeasance Securities Repaid in March 2016 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0	23,510
Total fixed rate | Loan Collateralized by Defeasance Securities Repaid in March 2016, 2 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0	66,183
Total fixed rate | Junior Mortgage Participation, Related To Mortgage Loan, February 2019 [Member]
Debt Investments Held [Abstract]
Loan acquired				5,700
Discount amount				$ 5,700
Total floating rate
Debt Investments Held [Abstract]
Future Funding Obligations	270,465
Senior Financing	2,955,153
Carrying Value	1,232,178	1,116,455
Total floating rate | Mezzanine Loan, with an Initial Maturity Date of June 2017 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	40,000
Carrying Value	15,369	68,977
Total floating rate | Mortgage/Mezzanine Loan with an Initial Maturity Date of January 2017 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	36,042
Senior Financing	0
Carrying Value	145,239	134,264
Total floating rate | Mezzanine Loan with an Initial Maturity Date of January 2017 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	118,949
Carrying Value	29,998	28,551
Total floating rate | Mortgage/Mezzanine Loan with an Initial Maturity Date of June 2017 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	32,847	0
Total floating rate | Mortgage/Mezzanine Loan with an Initial Maturity Date of July 2017 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	22,959	22,877
Total floating rate | Mortgage/Mezzanine Loan, September 2017 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	16,960	16,901
Total floating rate | Mortgage/Mezzanine Loan with an Initial Maturity Date of October 2017 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	3,479
Senior Financing	0
Carrying Value	20,423	19,282
Total floating rate | Mezzanine Loan with an Initial Maturity Date of November 2017 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	60,000
Carrying Value	14,957	14,904
Total floating rate | Mezzanine Loan with an Initial Maturity Date of December 2017 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	85,000
Carrying Value	15,141	29,505
Total floating rate | Mezzanine Loan with an Initial Maturity Date of December 2017, 2 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	65,000
Carrying Value	14,656	28,563
Total floating rate | Mortgage Mezzanine Loan with an Initial Maturity Date of December 2017 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	795
Senior Financing	0
Carrying Value	15,051	14,942
Total floating rate | Junior Mortgage Participation Loan with an Initial Maturity Date of April 2018 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	40,000
Carrying Value	19,913	19,846
Total floating rate | Mezzanine Loan with an Initial Maturity Date of April 2018 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	175,000
Carrying Value	34,844	34,725
Total floating rate | Mortgage/Mezzanine Loan, with an Initial Maturity Date of August 2018 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	523
Senior Financing	20,523
Carrying Value	10,863	31,210
Total floating rate | Mortgage Loan with an Initial Maturity Date of August 2018 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	19,840	0
Total floating rate | Mezzanine Loan with an Initial Maturity Date of August 2018 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	65,000
Carrying Value	14,880	0
Total floating rate | Mezzanine Loan with an Initial Maturity Date of September 2018 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	37,500
Carrying Value	14,648	0
Total floating rate | Mezzanine Loan with an Initial Maturity Date of October 2018 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	2,324
Senior Financing	45,025
Carrying Value	34,502	0
Total floating rate | Mezzanine Loan with an Initial Maturity Date of November 2018 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	335,000
Carrying Value	74,476	0
Total floating rate | Mezzanine Loan with an Initial Maturity Date of December 2018 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	33,000
Carrying Value	26,850	26,777
Total floating rate | Mezzanine Loan with an Initial Maturity Date of December 2018, 2 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	3,317
Senior Financing	165,326
Carrying Value	56,114	52,774
Total floating rate | Mezzanine Loan with an Initial Maturity Date of December 2018, 3 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	15,794
Senior Financing	259,229
Carrying Value	63,137	49,625
Total floating rate | Mezzanine Loan with an Initial Maturity Date of December 2018, 4 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	14,715
Senior Financing	199,935
Carrying Value	64,505	0
Total floating rate | Mezzanine Loan with an Initial Maturity Date of January 2019 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	45,000
Carrying Value	12,104	0
Total floating rate | Mezzanine Loan with an Initial Maturity Date of January 2019, 2 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	6,383
Senior Financing	16,383
Carrying Value	5,410	0
Total floating rate | Mezzanine Loan with an Initial Maturity of March 2019 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	38,000
Carrying Value	21,891	21,845
Total floating rate | Mezzanine Loan with an Initial Maturity Date of April 2019 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	265,000
Carrying Value	24,707	0
Total floating rate | Mortgage/Jr Mortgage Participate Loan, Maturity Date of August 2019 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	33,573
Senior Financing	183,300
Carrying Value	65,554	0
Total floating rate | Mezzanine Loan, Maturity of September 2019 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	2,500
Senior Financing	187,500
Carrying Value	37,322	0
Total floating rate | Mortgage/Mezzanine Loan with an Initial Maturity of September 2019 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	82,888
Senior Financing	0
Carrying Value	111,819	0
Total floating rate | Mortgage/Mezzanine Loan with an Initial Maturity of January 2020 [Member] [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	35,630
Senior Financing	0
Carrying Value	33,682	0
Total floating rate | Mezzanine Loan with an Initial Maturity of January 2020 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	32,502
Senior Financing	445,483
Carrying Value	125,911	0
Amount participated out	66,100
Total floating rate | Jr Mortgage Participation/Mezzanine Loan with an Initial Maturity of July 2021 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	30,000
Carrying Value	15,606	0
Total floating rate | Mezzanine Loan Repaid in December 2016 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0	49,751
Total floating rate | Mezzanine Loan Repaid in December 2016, 2 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0	13,731
Total floating rate | Mezzanine Loan Repaid in November 2016 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0	99,530
Total floating rate | Mortgage/Mezzanine Loan Repaid in September 2016 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0	94,901
Total floating rate | Jr Mortgage Participation/Mezzanine Loan Repaid in July 2016 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0	20,510
Total floating rate | Mezzanine Loan Repaid in June 2016 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0	22,625
Total floating rate | Mezzanine Loan Repaid in May 2016 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0	74,700
Total floating rate | Mezzanine Loan Contributed for a Joint Venture Interest [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0	66,398
Total floating rate | Jr. Mortgage Participation/Mezzanine Loan Repaid in March 2016 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0	18,395
Total floating rate | Mezzanine Loan Repaid in February 2016 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	$ 0	$ 40,346