Summary of Significant Accounting Policies - Schedule of Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value
Fair Value of Financial Instruments [Line Items]
Notes receivable from Preferred Operating Partnership unit holders	$ 113,683	$ 125,642
Fixed rate notes receivable	20,942	53,450
Fixed rate notes payable and notes payable to trusts	2,774,242	2,404,996
Exchangeable senior notes	719,056	706,827
Carrying Value
Fair Value of Financial Instruments [Line Items]
Notes receivable from Preferred Operating Partnership unit holders	120,230	120,230
Fixed rate notes receivable	20,608	52,201
Fixed rate notes payable and notes payable to trusts	2,815,085	2,417,558
Exchangeable senior notes	$ 624,259	$ 638,170