Mortgage Notes Payable - Schedule of Mortgage Notes Payable (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Mortgage loans payable on real estate [Line Items]
Carrying amount of mortgage notes, other	$ 4,560,810	$ 4,392,599
Chandler Fashion Center
Mortgage loans payable on real estate [Line Items]
Carrying amount of mortgage notes, other	$ 255,361	255,174
Effective interest rate (as a percent)	4.18%
Monthly debt service	$ 875
Danbury Fair Mall
Mortgage loans payable on real estate [Line Items]
Carrying amount of mortgage notes, other	$ 186,741	194,718
Effective interest rate (as a percent)	5.56%
Monthly debt service	$ 1,538
Fashion District Philadelphia
Mortgage loans payable on real estate [Line Items]
Carrying amount of mortgage notes, other	$ 201,000	0
Effective interest rate (as a percent)	4.00%
Monthly debt service	$ 670
Fashion Outlets of Chicago
Mortgage loans payable on real estate [Line Items]
Carrying amount of mortgage notes, other	$ 299,193	299,112
Effective interest rate (as a percent)	4.61%
Monthly debt service	$ 1,145
Fashion Outlets of Niagara Falls USA
Mortgage loans payable on real estate [Line Items]
Carrying amount of mortgage notes, other	$ 101,463	106,398
Effective interest rate (as a percent)	6.45%
Monthly debt service	$ 727
Freehold Raceway Mall
Mortgage loans payable on real estate [Line Items]
Carrying amount of mortgage notes, other	$ 398,545	398,379
Effective interest rate (as a percent)	3.94%
Monthly debt service	$ 1,300
Fresno Fashion Fair
Mortgage loans payable on real estate [Line Items]
Carrying amount of mortgage notes, other	$ 323,857	323,659
Effective interest rate (as a percent)	3.67%
Monthly debt service	$ 971
Green Acres Commons
Mortgage loans payable on real estate [Line Items]
Carrying amount of mortgage notes, other	$ 129,847	$ 128,926
Effective interest rate (as a percent)	2.87%	4.40%
Monthly debt service	$ 250
Green Acres Mall
Mortgage loans payable on real estate [Line Items]
Carrying amount of mortgage notes, other	$ 270,570	$ 277,747
Effective interest rate (as a percent)	3.61%
Monthly debt service	$ 1,447
Kings Plaza Shopping Center
Mortgage loans payable on real estate [Line Items]
Carrying amount of mortgage notes, other	$ 535,413	535,097
Effective interest rate (as a percent)	3.71%
Monthly debt service	$ 1,629
Oaks, The
Mortgage loans payable on real estate [Line Items]
Carrying amount of mortgage notes, other	$ 183,108	187,142
Effective interest rate (as a percent)	4.14%
Monthly debt service	$ 1,064
Pacific View
Mortgage loans payable on real estate [Line Items]
Carrying amount of mortgage notes, other	$ 114,909	118,202
Effective interest rate (as a percent)	4.08%
Monthly debt service	$ 668
Queens Center
Mortgage loans payable on real estate [Line Items]
Carrying amount of mortgage notes, other	$ 600,000	600,000
Effective interest rate (as a percent)	3.49%
Monthly debt service	$ 1,744
Santa Monica Place
Mortgage loans payable on real estate [Line Items]
Carrying amount of mortgage notes, other	$ 298,566	297,817
Effective interest rate (as a percent)	1.88%
Monthly debt service	$ 408
SanTan Village Regional Center
Mortgage loans payable on real estate [Line Items]
Carrying amount of mortgage notes, other	$ 219,233	219,140
Effective interest rate (as a percent)	4.34%
Monthly debt service	$ 788
Towne Mall
Mortgage loans payable on real estate [Line Items]
Carrying amount of mortgage notes, other	$ 19,815	20,284
Effective interest rate (as a percent)	4.48%
Monthly debt service	$ 117
Tucson La Encantada
Mortgage loans payable on real estate [Line Items]
Carrying amount of mortgage notes, other	$ 62,018	63,682
Effective interest rate (as a percent)	4.23%
Monthly debt service	$ 368
Victor Valley, Mall of
Mortgage loans payable on real estate [Line Items]
Carrying amount of mortgage notes, other	$ 114,791	114,733
Effective interest rate (as a percent)	4.00%
Monthly debt service	$ 380
Vintage Faire Mall
Mortgage loans payable on real estate [Line Items]
Carrying amount of mortgage notes, other	$ 246,380	$ 252,389
Effective interest rate (as a percent)	3.55%
Monthly debt service	$ 1,256