Debt and Preferred Equity Investments (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Feb. 28, 2017	Dec. 31, 2016	Sep. 30, 2014
Debt investment
Increase in debt and preferred equity investments (net of discounts), including investments classified as held-for-sale	$ 1,000,000	$ 255,000
Decrease in debt and preferred equity investments (net of discounts), including investments classified as held-for-sale	$ 656,900	$ 567,900
Aggregate weighted average current yield (as a percent)	9.73%
Debt Investments Held [Abstract]
Carrying Value	$ 1,986,413			$ 1,640,412
Mezzanine/Jr. Mortgage Loan with an Initial Maturity Date of April 2017
Debt Investments Held [Abstract]
Debt instrument, accrued interest	6,200
Mezzanine Loan with an Initial Maturity Date of March 2020
Debt Investments Held [Abstract]
Amount participated out	1,200
Mezzanine Loan, with an Initial Maturity Date of June 2017
Debt Investments Held [Abstract]
Amount participated out	12,000
Mezzanine Loan with an Initial Maturity Date of December 2017
Debt Investments Held [Abstract]
Amount participated out	14,600
Mezzanine Loan with an Initial Maturity Date of December 2017, 2
Debt Investments Held [Abstract]
Amount participated out	14,100
Mortgage Mezzanine Loan with an Initial Maturity Date of December 2017
Debt Investments Held [Abstract]
Amount participated out	5,100
Debt Investments in Mortgage Loans
Debt Investments Held [Abstract]
Future Funding Obligations	214,255
Senior Financing	6,909,095
Carrying Value	1,843,094			1,592,537
Total fixed rate
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	3,672,474
Carrying Value	630,611			360,359
Total fixed rate | Mezzanine/Jr. Mortgage Loan with an Initial Maturity Date of April 2017
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	250,150			0
Total fixed rate | Mortgage Loan, February 2019
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	26,338			26,311
Loan acquired					$ 26,400
Discount amount					200
Total fixed rate | Mortgage Loan, August 2019
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	311			380
Total fixed rate | Mezzanine Loan with an Initial Maturity Date of March 2020
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	1,160,000
Carrying Value	199,533			0
Total fixed rate | Mezzanine Loan, September 2021
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 April 2022
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	147,000
Carrying Value	24,905			0
Total fixed rate | Mezzanine Loan, November 2023
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	87,724
Carrying Value	12,696			12,692
Total fixed rate | Mezzanine Loan, with an Initial Maturity Date of June 2017
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	115,000
Carrying Value	12,928			12,925
Total fixed rate | Mezzanine Loan, January 2025
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
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	340,000
Carrying Value	15,000			15,000
Total fixed rate | Mezzanine Loan with an Initial Maturity Date of June 2027
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	1,712,750
Carrying Value	55,250			0
Total fixed rate | Mezzanine Loan, June 2017
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0			66,129
Total fixed rate | Junior Mortgage Participation/Mezzanine Loan, March 2017
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0			193,422
Total fixed rate | Junior Mortgage Participation, Related To Mortgage Loan, February 2019
Debt Investments Held [Abstract]
Loan acquired					5,700
Discount amount					$ 5,700
Total floating rate
Debt Investments Held [Abstract]
Future Funding Obligations	214,255
Senior Financing	3,236,621
Carrying Value	1,212,483			1,232,178
Total floating rate | Mezzanine Loan, with an Initial Maturity Date of September 2017
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	40,000
Carrying Value	15,442			15,369
Total floating rate | Mortgage/Mezzanine Loan, September 2017
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	16,989			16,960
Total floating rate | Mortgage/Mezzanine Loan with an Initial Maturity Date of October 2017
Debt Investments Held [Abstract]
Future Funding Obligations	1,361
Senior Financing	0
Carrying Value	22,602			20,423
Total floating rate | Mezzanine Loan with an Initial Maturity Date of December 2017
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	85,000
Carrying Value	15,273			15,141
Total floating rate | Mezzanine Loan with an Initial Maturity Date of December 2017, 2
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	65,000
Carrying Value	14,773			14,656
Total floating rate | Mortgage Mezzanine Loan with an Initial Maturity Date of December 2017
Debt Investments Held [Abstract]
Future Funding Obligations	795
Senior Financing	0
Carrying Value	15,105			15,051
Total floating rate | Mortgage/Mezzanine Loan with an Initial Maturity Date of January 2018
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	125,000
Carrying Value	29,934			29,998
Total floating rate | Mezzanine Loan with an Initial Maturity Date of April 2018
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	40,000
Carrying Value	19,947			19,913
Total floating rate | Junior Mortgage Participation Loan with an Initial Maturity Date of April 2018
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	175,000
Carrying Value	34,903			34,844
Total floating rate | Mezzanine Loan with an Initial Maturity Date of August 2018
Debt Investments Held [Abstract]
Future Funding Obligations	523
Senior Financing	20,523
Carrying Value	10,898			10,863
Total floating rate | Mortgage/Mezzanine Loan, with an Initial Maturity Date of August 2018
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	19,889			19,840
Total floating rate | Mortgage Loan with an Initial Maturity Date of August 2018
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	65,000
Carrying Value	14,916			14,880
Total floating rate | Mezzanine Loan with an Initial Maturity Date of September 2018
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	37,500
Carrying Value	14,749			14,648
Total floating rate | Mezzanine Loan with an Initial Maturity Date of October 2018
Debt Investments Held [Abstract]
Future Funding Obligations	2,325
Senior Financing	45,025
Carrying Value	34,686			34,502
Total floating rate | Mezzanine Loan with an Initial Maturity Date of November 2018
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	335,000
Carrying Value	74,612			74,476
Total floating rate | Mezzanine Loan with an Initial Maturity Date of December 2018
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	33,000
Carrying Value	26,888			26,850
Total floating rate | Mezzanine Loan with an Initial Maturity Date of December 2018, 2
Debt Investments Held [Abstract]
Future Funding Obligations	1,122
Senior Financing	171,728
Carrying Value	58,451			56,114
Total floating rate | Mezzanine Loan with an Initial Maturity Date of December 2018, 3
Debt Investments Held [Abstract]
Future Funding Obligations	10,758
Senior Financing	279,563
Carrying Value	68,437			63,137
Total floating rate | Mezzanine Loan with an Initial Maturity Date of December 2018, 4
Debt Investments Held [Abstract]
Future Funding Obligations	7,651
Senior Financing	221,568
Carrying Value	71,760			64,505
Total floating rate | Mezzanine Loan with an Initial Maturity Date of January 2019
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	45,000
Carrying Value	12,138			12,104
Total floating rate | Mortgage/Mezzanine Loan with an Initial Maturity Date of January 2019
Debt Investments Held [Abstract]
Future Funding Obligations	38,087
Senior Financing	0
Carrying Value	175,792			0
Total floating rate | Mezzanine Loan with an Initial Maturity of January 2019, 2
Debt Investments Held [Abstract]
Future Funding Obligations	7,277
Senior Financing	19,733
Carrying Value	6,588			5,410
Total floating rate | Mezzanine Loan with an Initial Maturity of March 2019
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	38,000
Carrying Value	21,915			21,891
Total floating rate | Mezzanine Loan with an Initial Maturity Date of April 2019
Debt Investments Held [Abstract]
Future Funding Obligations	513
Senior Financing	172,604
Carrying Value	36,655			0
Total floating rate | Mezzanine Loan with an Initial Maturity Date of April 2019, 2 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	265,000
Carrying Value	24,767			24,707
Total floating rate | Mortgage/Jr Mortgage Participate Loan, Maturity Date of August 2019
Debt Investments Held [Abstract]
Future Funding Obligations	31,628
Senior Financing	188,664
Carrying Value	67,655			65,554
Total floating rate | Mezzanine Loan, Maturity of September 2019
Debt Investments Held [Abstract]
Future Funding Obligations	2,500
Senior Financing	187,500
Carrying Value	37,353			37,322
Total floating rate | Mortgage/Mezzanine Loan with an Initial Maturity of September 2019
Debt Investments Held [Abstract]
Future Funding Obligations	64,691
Senior Financing	0
Carrying Value	130,067			111,819
Total floating rate | Mortgage/Mezzanine Loan with an Initial Maturity of January 2020
Debt Investments Held [Abstract]
Future Funding Obligations	35,106
Senior Financing	0
Carrying Value	34,271			33,682
Total floating rate | Mezzanine Loan with an Initial Maturity of January 2020
Debt Investments Held [Abstract]
Future Funding Obligations	9,918
Senior Financing	521,213
Carrying Value	69,408		$ 66,100	125,911
Total floating rate | Jr Mortgage Participation/Mezzanine Loan with an Initial Maturity of July 2021
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	60,000
Carrying Value	15,620			15,606
Total floating rate | Mortgage/Mezzanine Loan repaid in June 2017, 2
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0			32,847
Total floating rate | Mortgage/Mezzanine Loan repaid in June 2017
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0			22,959
Total floating rate | Mezzanine Loan Contributed for a Joint Venture Interest
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0			14,957
Total floating rate | Mortgage/Mezzanine Loan Repaid in January 2017
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	$ 0			$ 145,239