Debt and Preferred Equity Investments (Details) - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 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	$ 403,900,000	$ 128,800,000
Decrease in debt and preferred equity investments (net of discounts), including investments classified as held-for-sale	$ 416,500,000	$ 420,200,000
Aggregate weighted average current yield (as a percent)	9.42%
Debt Investments Held [Abstract]
Carrying Value, Net of Discounts and Deferred Origination Fees	$ 1,627,836,000			$ 1,640,412,000
Junior Mortgage Participation Acquired in September 2014 [Member]
Debt Investments Held [Abstract]
Carrying Value, Net of Discounts and Deferred Origination Fees	0			0
Mezzanine Loan, June 2017
Debt Investments Held [Abstract]
Amount participated out	41,300,000
Mezzanine Loan, June 2024
Debt Investments Held [Abstract]
Amount participated out	12,000,000
Mortgage/Mezzanine Loan, June 2017
Debt Investments Held [Abstract]
Amount participated out	14,500,000
Mezzanine Loan with an Initial Maturity Date of December 2017 [Member]
Debt Investments Held [Abstract]
Amount participated out	14,600,000
Mezzanine Loan with an Initial Maturity Date of December 2017, 2 [Member]
Debt Investments Held [Abstract]
Amount participated out	14,100,000
Mortgage Mezzanine Loan with an Initial Maturity Date of December 2017 [Member]
Debt Investments Held [Abstract]
Amount participated out	5,100,000
Debt Investments in Mortgage Loans [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	241,683,000
Senior Financing	5,386,263,000
Carrying Value, Net of Discounts and Deferred Origination Fees	1,579,930,000			1,592,537,000
Total fixed rate
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	2,314,991,000
Carrying Value, Net of Discounts and Deferred Origination Fees	364,345,000			360,359,000
Total fixed rate | Junior Mortgage Participation/Mezzanine Loan, March 2017
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value, Net of Discounts and Deferred Origination Fees	0			193,422,000
Total fixed rate | Mezzanine Loan, June 2017
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	502,100,000
Carrying Value, Net of Discounts and Deferred Origination Fees	66,197,000			66,129,000
Total fixed rate | Mortgage Loan, February 2019
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value, Net of Discounts and Deferred Origination Fees	26,324,000			26,311,000
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	346,000			380,000
Total fixed rate | Mezzanine Loan with an Initial Maturity Date of March 2020 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	1,160,000,000
Carrying Value, Net of Discounts and Deferred Origination Fees	197,358,000			0
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			3,500,000
Total fixed rate | Mezzanine Loan, November 2023
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	87,891,000
Carrying Value, Net of Discounts and Deferred Origination Fees	12,694,000			12,692,000
Total fixed rate | Mezzanine Loan, June 2024
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	115,000,000
Carrying Value, Net of Discounts and Deferred Origination Fees	12,926,000			12,925,000
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			30,000,000
Total fixed rate | Mezzanine Loan with an Initial Maturity Date of November 2026 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	340,000,000
Carrying Value, Net of Discounts and Deferred Origination Fees	15,000,000			15,000,000
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	241,683,000
Senior Financing	3,071,272,000
Carrying Value, Net of Discounts and Deferred Origination Fees	1,215,585,000			1,232,178,000
Total floating rate | Mezzanine Loan, June 2017
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value, Net of Discounts and Deferred Origination Fees	32,929,000			32,847,000
Total floating rate | Mortgage/Mezzanine Loan, with an Initial Maturity Date of August 2018 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	523,000
Senior Financing	20,523,000
Carrying Value, Net of Discounts and Deferred Origination Fees	10,880,000			10,863,000
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, Net of Discounts and Deferred Origination Fees	19,864,000			19,840,000
Total floating rate | Mezzanine Loan with an Initial Maturity Date of August 2018 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	65,000,000
Carrying Value, Net of Discounts and Deferred Origination Fees	14,898,000			14,880,000
Total floating rate | Mezzanine Loan with an Initial Maturity Date of September 2018 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	37,500,000
Carrying Value, Net of Discounts and Deferred Origination Fees	14,698,000			14,648,000
Total floating rate | Mezzanine Loan with an Initial Maturity Date of October 2018 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	2,325,000
Senior Financing	45,025,000
Carrying Value, Net of Discounts and Deferred Origination Fees	34,593,000			34,502,000
Total floating rate | Mezzanine Loan with an Initial Maturity Date of November 2018 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	335,000,000
Carrying Value, Net of Discounts and Deferred Origination Fees	74,543,000			74,476,000
Total floating rate | Mezzanine Loan with an Initial Maturity Date of December 2018 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	33,000,000
Carrying Value, Net of Discounts and Deferred Origination Fees	26,868,000			26,850,000
Total floating rate | Mezzanine Loan with an Initial Maturity Date of December 2018, 2 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	2,005,000
Senior Financing	169,152,000
Carrying Value, Net of Discounts and Deferred Origination Fees	57,496,000			56,114,000
Total floating rate | Mezzanine Loan with an Initial Maturity Date of December 2018, 3 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	14,191,000
Senior Financing	265,704,000
Carrying Value, Net of Discounts and Deferred Origination Fees	64,870,000			63,137,000
Total floating rate | Mezzanine Loan with an Initial Maturity Date of December 2018, 4 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	11,177,000
Senior Financing	210,770,000
Carrying Value, Net of Discounts and Deferred Origination Fees	68,136,000			64,505,000
Total floating rate | Mezzanine Loan with an Initial Maturity Date of January 2019 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	45,000,000
Carrying Value, Net of Discounts and Deferred Origination Fees	12,120,000			12,104,000
Total floating rate | Mezzanine Loan with an Initial Maturity Date of January 2019, 2 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	42,548,000
Senior Financing	0
Carrying Value, Net of Discounts and Deferred Origination Fees	171,352,000			0
Total floating rate | Mezzanine Loan with an Initial Maturity of January 2019, 3 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	6,383,000
Senior Financing	16,383,000
Carrying Value, Net of Discounts and Deferred Origination Fees	5,434,000			5,410,000
Total floating rate | Mezzanine Loan with an Initial Maturity of March 2019 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	38,000,000
Carrying Value, Net of Discounts and Deferred Origination Fees	21,903,000			21,891,000
Total floating rate | Mezzanine Loan with an Initial Maturity Date of April 2019 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	265,000,000
Carrying Value, Net of Discounts and Deferred Origination Fees	24,736,000			24,707,000
Total floating rate | Mortgage/Jr Mortgage Participate Loan, Maturity Date of August 2019 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	32,721,000
Senior Financing	185,649,000
Carrying Value, Net of Discounts and Deferred Origination Fees	66,484,000			65,554,000
Total floating rate | Mezzanine Loan, Maturity of September 2019 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	2,500,000
Senior Financing	187,500,000
Carrying Value, Net of Discounts and Deferred Origination Fees	37,337,000			37,322,000
Total floating rate | Mortgage/Mezzanine Loan with an Initial Maturity of September 2019 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	75,310,000
Senior Financing	0
Carrying Value, Net of Discounts and Deferred Origination Fees	119,422,000			111,819,000
Total floating rate | Mortgage/Mezzanine Loan with an Initial Maturity of January 2020 [Member] [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	35,630,000
Senior Financing	0
Carrying Value, Net of Discounts and Deferred Origination Fees	33,714,000			33,682,000
Total floating rate | Mezzanine Loan with an Initial Maturity of January 2020 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	13,273,000
Senior Financing	502,066,000
Carrying Value, Net of Discounts and Deferred Origination Fees	65,993,000		$ 66,100,000	125,911,000
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	60,000,000
Carrying Value, Net of Discounts and Deferred Origination Fees	15,613,000			15,606,000
Total floating rate | Mezzanine Loan Repaid in December 2016 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value, Net of Discounts and Deferred Origination Fees	0			145,239,000
Total floating rate | Mortgage/Mezzanine Loan, June 2017
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	40,000,000
Carrying Value, Net of Discounts and Deferred Origination Fees	15,446,000			15,369,000
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, Net of Discounts and Deferred Origination Fees	22,978,000			22,959,000
Total floating rate | Mortgage/Mezzanine Loan, September 2017 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value, Net of Discounts and Deferred Origination Fees	16,975,000			16,960,000
Total floating rate | Mortgage/Mezzanine Loan with an Initial Maturity Date of October 2017 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	2,302,000
Senior Financing	0
Carrying Value, Net of Discounts and Deferred Origination Fees	21,630,000			20,423,000
Total floating rate | Mezzanine Loan with an Initial Maturity Date of November 2017 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	60,000,000
Carrying Value, Net of Discounts and Deferred Origination Fees	14,970,000			14,957,000
Total floating rate | Mezzanine Loan with an Initial Maturity Date of December 2017 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	85,000,000
Carrying Value, Net of Discounts and Deferred Origination Fees	15,206,000			15,141,000
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	65,000,000
Carrying Value, Net of Discounts and Deferred Origination Fees	14,714,000			14,656,000
Total floating rate | Mortgage Mezzanine Loan with an Initial Maturity Date of December 2017 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	795,000
Senior Financing	0
Carrying Value, Net of Discounts and Deferred Origination Fees	15,078,000			15,051,000
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	125,000,000
Carrying Value, Net of Discounts and Deferred Origination Fees	29,902,000			29,998,000
Total floating rate | Mezzanine Loan with an Initial Maturity Date of April 2018 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	40,000,000
Carrying Value, Net of Discounts and Deferred Origination Fees	19,930,000			19,913,000
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	175,000,000
Carrying Value, Net of Discounts and Deferred Origination Fees	$ 34,873,000			$ 34,844,000