Summary of Significant Accounting Policies - Recent Accounting Pronouncements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2019	Jan. 01, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Investments in unconsolidated joint ventures	$ 0	$ 31,150
Financing arrangement obligation	378,485	0
Accumulated deficit	(1,614,357)	(830,279)
Capitalized internal leasing costs	22,536	22,403	$ 25,788
Net cash provided by investing activities	$ 176,323	178,988	454,066
ASU 2016-18
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net cash provided by investing activities		$ 2,116	$ 8,562
Joint venture | Financing arrangement | ASU 2014-09 | Difference between revenue guidance in effect before and after topic 606 | Freehold Raceway Mall and Chandler Fashion Center
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Financing arrangement obligation					$ 393,709
Accumulated deficit					424,859
Joint venture | Freehold Raceway Mall and Chandler Fashion Center
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Investments in unconsolidated joint ventures					$ 31,150
Minimum | ASU 2016-02 | Forecast
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Right of use asset				$ 110,000
Lease liability				100,000
Maximum | ASU 2016-02 | Forecast
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Right of use asset				130,000
Lease liability				$ 120,000