Equity Investments in Real Estate - Summarized Investee Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Equity Method Investment, Summarized Financial Information
Net investments in real estate	$ 3,850,204	$ 3,569,612
Other assets	595,352	497,198
Total assets	4,445,556	4,066,810
Debt	2,584,248	2,619,153
Accounts payable, accrued expenses and other liabilities	374,040	447,944
Total liabilities	2,958,288	3,067,097
Total equity	$ 1,487,268	$ 999,713