Fair Value of Financial Instruments - Investment in Securities and Debt (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Non-real estate investments measured at fair value	$ 133,790	$ 135,115
Carrying Value | Unsecured debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	1,925,000	1,925,000
Carrying Value | Secured debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	1,560,093	1,507,276
Carrying Value | In-substance defeased debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	130,828	131,707
Carrying Value | Joint venture partner debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	66,136	66,136
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Non-real estate investments measured at fair value	138,903	140,270
Fair Value | Unsecured debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	2,006,648	2,072,833
Fair Value | Secured debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	1,556,953	1,503,960
Fair Value | In-substance defeased debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	130,783	131,633
Fair Value | Joint venture partner debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	$ 68,831	$ 68,346