Mortgage Notes Payable - Schedule of Mortgage Notes Payable (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Jun. 27, 2019	Jan. 10, 2019	Dec. 31, 2018
Mortgage loans payable on real estate
Carrying amount of mortgage notes, other	$ 4,392,599			$ 4,073,916
Chandler Fashion Center
Mortgage loans payable on real estate
Carrying amount of mortgage notes, other	$ 255,174			199,972
Effective interest rate (as a percent)	4.18%	4.18%
Monthly debt service	$ 875
Danbury Fair Mall
Mortgage loans payable on real estate
Carrying amount of mortgage notes, other	$ 194,718			202,158
Effective interest rate (as a percent)	5.53%
Monthly debt service	$ 1,538
Fashion Outlets of Chicago
Mortgage loans payable on real estate
Carrying amount of mortgage notes, other	$ 299,112			199,622
Effective interest rate (as a percent)	4.61%		4.61%
Monthly debt service	$ 1,145
Fashion Outlets of Niagara Falls USA
Mortgage loans payable on real estate
Carrying amount of mortgage notes, other	$ 106,398			109,651
Effective interest rate (as a percent)	4.89%
Monthly debt service	$ 727
Freehold Raceway Mall
Mortgage loans payable on real estate
Carrying amount of mortgage notes, other	$ 398,379			398,212
Effective interest rate (as a percent)	3.94%
Monthly debt service	$ 1,300
Fresno Fashion Fair
Mortgage loans payable on real estate
Carrying amount of mortgage notes, other	$ 323,659			323,460
Effective interest rate (as a percent)	3.67%
Monthly debt service	$ 971
Green Acres Commons
Mortgage loans payable on real estate
Carrying amount of mortgage notes, other	$ 128,926			$ 128,006
Effective interest rate (as a percent)	4.40%			5.06%
Monthly debt service	$ 416
Green Acres Mall
Mortgage loans payable on real estate
Carrying amount of mortgage notes, other	$ 277,747			$ 284,686
Effective interest rate (as a percent)	3.61%
Monthly debt service	$ 1,447
Kings Plaza Shopping Center
Mortgage loans payable on real estate
Carrying amount of mortgage notes, other	$ 535,097			437,120
Effective interest rate (as a percent)	3.71%
Monthly debt service	$ 1,629
Oaks, The
Mortgage loans payable on real estate
Carrying amount of mortgage notes, other	$ 187,142			192,037
Effective interest rate (as a percent)	4.14%
Monthly debt service	$ 1,064
Pacific View
Mortgage loans payable on real estate
Carrying amount of mortgage notes, other	$ 118,202			121,362
Effective interest rate (as a percent)	4.08%
Monthly debt service	$ 668
Queens Center
Mortgage loans payable on real estate
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
Carrying amount of mortgage notes, other	$ 297,817			297,069
Effective interest rate (as a percent)	3.34%
Monthly debt service	$ 772
SanTan Village Regional Center
Mortgage loans payable on real estate
Carrying amount of mortgage notes, other	$ 219,140			121,585
Effective interest rate (as a percent)	4.34%
Monthly debt service	$ 788
Towne Mall
Mortgage loans payable on real estate
Carrying amount of mortgage notes, other	$ 20,284			20,733
Effective interest rate (as a percent)	4.48%
Monthly debt service	$ 117
Tucson La Encantada
Mortgage loans payable on real estate
Carrying amount of mortgage notes, other	$ 63,682			65,361
Effective interest rate (as a percent)	4.23%
Monthly debt service	$ 368
Victor Valley, Mall of
Mortgage loans payable on real estate
Carrying amount of mortgage notes, other	$ 114,733			114,675
Effective interest rate (as a percent)	4.00%
Monthly debt service	$ 380
Vintage Faire Mall
Mortgage loans payable on real estate
Carrying amount of mortgage notes, other	$ 252,389			$ 258,207
Effective interest rate (as a percent)	3.55%
Monthly debt service	$ 1,256