Debt and Preferred Equity Investments - Additional Information (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Aggregate weighted average current yield (as a percent)	9.00%
Debt Investments Held [Abstract]
Carrying Value	$ 2,228,912	$ 2,099,393
Mezzanine Loan with an Initial Maturity Date of March 2020
Debt Investments Held [Abstract]
Amount participated out	1,300
Mezzanine Loan, with an Initial Maturity Date of June 2024
Debt Investments Held [Abstract]
Amount participated out	12,000
Debt Investments in Mortgage Loans
Debt Investments Held [Abstract]
Future Funding Obligations	183,109
Senior Financing	6,853,921
Carrying Value	1,989,792	1,812,936
Total fixed rate
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	4,108,910
Carrying Value	631,439	430,099
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	217,891	213,185
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	24,941	24,932
Total fixed rate | Mezzanine Loan with an Initial Maturity of August 2022
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	280,000
Carrying Value	37,630	36,585
Total fixed rate | Mezzanine Loan With Maturity June 2023
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	319,551
Carrying Value	206,572	0
Total fixed rate | Mezzanine Loan, November 2023
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	84,609
Carrying Value	12,710	12,706
Total fixed rate | Mezzanine Loan With An Initial Maturity Date Of December 2023
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	180,000
Carrying Value	30,000	30,000
Total fixed rate | Mezzanine Loan, with an Initial Maturity Date of June 2024
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	115,000
Carrying Value	12,945	12,941
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 June 2027
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	1,712,750
Carrying Value	55,250	55,250
Total fixed rate | Mezzanine Loan Sold In 2019
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0	11,000
Total floating rate
Debt Investments Held [Abstract]
Future Funding Obligations	183,109
Senior Financing	2,745,011
Carrying Value	1,358,353	1,382,837
Total floating rate | Mezzanine Loan with an Initial Maturity Date of March 2020
Debt Investments Held [Abstract]
Future Funding Obligations	387
Senior Financing	327,634
Carrying Value	54,427	53,402
Total floating rate | Mezzanine Loan With An Initial Maturity May 2019
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	142,000
Carrying Value	30,000	15,333
Total floating rate | Mezzanine Loan With An Initial Maturity May 2019, 2
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	29,000	14,822
Total floating rate | Mortgage/Jr Mortgage Participate Loan, Maturity Date of August 2019
Debt Investments Held [Abstract]
Future Funding Obligations	38,203
Senior Financing	239,507
Carrying Value	86,512	84,012
Total floating rate | Mortgage/Mezzanine Loan With An Initial Maturity Date Of August 2019
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	20,000	19,999
Total floating rate | Mortgage/Mezzanine Loan with an Initial Maturity of September 2019
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	119,963	154,070
Total floating rate | Mezzanine Loan with an Initial Maturity of October 2019
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	350,000
Carrying Value	34,961	34,886
Total floating rate | Mortgage/Mezzanine Loan with an Initial Maturity of January 2020
Debt Investments Held [Abstract]
Future Funding Obligations	13,237
Senior Financing	39,597
Carrying Value	91,904	62,493
Total floating rate | Mezzanine Loan with an Initial Maturity of January 2020
Debt Investments Held [Abstract]
Future Funding Obligations	1
Senior Financing	579,997
Carrying Value	94,677	79,164
Total floating rate | Mortgage Loan with an Initial Maturity of February 2020
Debt Investments Held [Abstract]
Future Funding Obligations	7,603
Senior Financing	0
Carrying Value	92,237	88,501
Total floating rate | Mortgage/Mezzanine Loan Due March 2020
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	69,484	0
Total floating rate | Mortgage and Mezzanine Loan with an Initial Maturity Date of April 2020
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	40,000
Carrying Value	19,999	19,986
Total floating rate | Mortgage And Mezzanine Loan With An Initial Maturity Date Of June 2020
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	49,470
Carrying Value	19,321	37,094
Total floating rate | Mezzanine Loan with an Initial Maturity of July 2020
Debt Investments Held [Abstract]
Future Funding Obligations	6,547
Senior Financing	42,174
Carrying Value	13,980	12,627
Total floating rate | Mortgage And Mezzanine Loan With An Initial Maturity Date Of October 2020
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	64,147
Carrying Value	55,129	83,449
Total floating rate | Mezzanine Loan with an Initial Maturity of November 2020
Debt Investments Held [Abstract]
Future Funding Obligations	32,295
Senior Financing	388,264
Carrying Value	95,360	88,817
Total floating rate | Mortgage/Mezzanine Loan with an Initial Maturity of December 2020
Debt Investments Held [Abstract]
Future Funding Obligations	25,597
Senior Financing	0
Carrying Value	106,579	98,804
Total floating rate | Mortgage/Mezzanine Loan with an Initial Maturity of December 2020, 2
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	35,325	35,266
Total floating rate | Mortgage/Mezzanine Loan With An Initial Maturity Due April 2021
Debt Investments Held [Abstract]
Future Funding Obligations	35,358
Senior Financing	0
Carrying Value	193,664	277,694
Total floating rate | Mezzanine Loan With An Initial Maturity Due April 2021
Debt Investments Held [Abstract]
Future Funding Obligations	9,750
Senior Financing	275,000
Carrying Value	39,987	24,961
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	15,681	15,665
Total floating rate | Mezzanine Loan With An Initial Maturity Due July 2021
Debt Investments Held [Abstract]
Future Funding Obligations	14,131
Senior Financing	147,221
Carrying Value	40,163	0
Total floating rate | Mezzanine Loan Repaid In 2019
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0	7,305
Total floating rate | Mezzanine Loan Repaid In 2019, 2
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0	14,998
Total floating rate | Mezzanine Loan Repaid In 2019, 3
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0	21,990
Total floating rate | Mezzanine Loan Repaid In 2019, 4
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	$ 0	$ 37,499