Mortgage Notes Payable - Schedule of mortgage notes payable (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Mortgage loans payable on real estate
Long-term Debt	$ 4,534,585	$ 4,560,810
Chandler Fashion Center
Mortgage loans payable on real estate
Long-term Debt	$ 255,407	255,361
Effective Interest Rate	4.18%
Monthly Debt Service	$ 875
Danbury Fair Mall
Mortgage loans payable on real estate
Long-term Debt	$ 184,775	186,741
Effective Interest Rate	5.56%
Monthly Debt Service	$ 1,538
Fashion District Philadelphia
Mortgage loans payable on real estate
Long-term Debt	$ 201,000	201,000
Effective Interest Rate	4.00%
Monthly Debt Service	$ 670
Fashion Outlets of Chicago
Mortgage loans payable on real estate
Long-term Debt	$ 299,213	299,193
Effective Interest Rate	4.61%
Monthly Debt Service	$ 1,145
Fashion Outlets of Niagara Falls USA
Mortgage loans payable on real estate
Long-term Debt	$ 100,820	101,463
Effective Interest Rate	6.45%
Monthly Debt Service	$ 727
Freehold Raceway Mall
Mortgage loans payable on real estate
Long-term Debt	$ 398,588	398,545
Effective Interest Rate	3.94%
Monthly Debt Service	$ 1,300
Fresno Fashion Fair
Mortgage loans payable on real estate
Long-term Debt	$ 323,907	323,857
Effective Interest Rate	3.67%
Monthly Debt Service	$ 971
Green Acres Commons
Mortgage loans payable on real estate
Long-term Debt	$ 124,631	129,847
Effective Interest Rate	3.13%
Monthly Debt Service	$ 299
Green Acres Mall
Mortgage loans payable on real estate
Long-term Debt	$ 257,115	270,570
Effective Interest Rate	3.94%
Monthly Debt Service	$ 1,447
Kings Plaza Shopping Center
Mortgage loans payable on real estate
Long-term Debt	$ 535,542	535,413
Effective Interest Rate	3.71%
Monthly Debt Service	$ 1,629
Oaks, The
Mortgage loans payable on real estate
Long-term Debt	$ 180,731	183,108
Effective Interest Rate	4.14%
Monthly Debt Service	$ 1,064
Pacific View
Mortgage loans payable on real estate
Long-term Debt	$ 114,065	114,909
Effective Interest Rate	4.08%
Monthly Debt Service	$ 668
Queens Center
Mortgage loans payable on real estate
Long-term Debt	$ 600,000	600,000
Effective Interest Rate	3.49%
Monthly Debt Service	$ 1,744
Santa Monica Place
Mortgage loans payable on real estate
Long-term Debt	$ 298,753	$ 298,566
Effective Interest Rate	1.83%	1.88%
Monthly Debt Service	$ 395
SanTan Village Regional Center
Mortgage loans payable on real estate
Long-term Debt	$ 219,254	$ 219,233
Effective Interest Rate	4.34%
Monthly Debt Service	$ 788
Towne Mall
Mortgage loans payable on real estate
Long-term Debt	$ 19,690	19,815
Effective Interest Rate	4.48%
Monthly Debt Service	$ 117
Tucson La Encantada
Mortgage loans payable on real estate
Long-term Debt	$ 61,480	62,018
Effective Interest Rate	4.23%
Monthly Debt Service	$ 368
Victor Valley, Mall of
Mortgage loans payable on real estate
Long-term Debt	$ 114,806	114,791
Effective Interest Rate	4.00%
Monthly Debt Service	$ 380
Vintage Faire Mall
Mortgage loans payable on real estate
Long-term Debt	$ 244,808	$ 246,380
Effective Interest Rate	3.55%
Monthly Debt Service	$ 1,256