Debt and Preferred Equity Investments - Preferred Equity Investments (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Preferred equity investment
Aggregate weighted average current yield (as a percent)	8.89%
Carrying Value	$ 1,954,556	$ 2,099,393
Preferred Equity, April 2021
Preferred equity investment
Future Funding Obligations	0
Senior Financing	272,000
Carrying Value	143,614	143,183
Preferred Equity, June 2022
Preferred equity investment
Future Funding Obligations	0
Senior Financing	1,763,271
Carrying Value	$ 96,895	143,274
Preferred equity investments
Preferred equity investment
Aggregate weighted average current yield (as a percent)	9.51%
Future Funding Obligations	$ 0
Senior Financing	2,035,271
Carrying Value	$ 240,509	$ 286,457