Debt and Preferred Equity Investments - Preferred Equity Investments (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Preferred equity investment
Aggregate weighted average current yield (as a percent)	9.49%
Carrying Value	$ 2,020,739	$ 1,640,412
Preferred Equity, April 2021
Preferred equity investment
Future Funding Obligations	0
Senior Financing	272,000
Carrying Value	143,980	0
Preferred Equity redeemed in May 2017
Preferred equity investment
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0	9,982
Preferred Equity redeemed in April 2017
Preferred equity investment
Future Funding Obligations	0
Senior Financing	0
Carrying Value	$ 0	37,893
Preferred equity investments
Preferred equity investment
Aggregate weighted average current yield (as a percent)	6.98%
Future Funding Obligations	$ 0
Senior Financing	272,000
Carrying Value	$ 143,980	$ 47,875