Debt and Preferred Equity Investments - Preferred Equity Investments (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Preferred equity investment
Aggregate weighted average current yield (as a percent)	9.00%
Carrying Value	$ 2,228,912	$ 2,099,393
Preferred Equity, April 2021
Preferred equity investment
Future Funding Obligations	0
Senior Financing	272,000
Carrying Value	143,380	143,183
Preferred Equity, June 2022
Preferred equity investment
Future Funding Obligations	0
Senior Financing	1,763,014
Carrying Value	$ 95,740	143,274
Preferred equity investments
Preferred equity investment
Aggregate weighted average current yield (as a percent)	9.51%
Future Funding Obligations	$ 0
Senior Financing	2,035,014
Carrying Value	$ 239,120	$ 286,457