Mortgage Notes Payable - Schedule of Mortgage Notes Payable (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	May. 12, 2015	Feb. 19, 2015	Dec. 31, 2014
Mortgage loans payable on real estate
Carrying Amount of Mortgage Notes, Related Party	$ 282,413			$ 289,039
Carrying Amount of Mortgage Notes, Other	5,407,170			5,115,482
Arrowhead Towne Center
Mortgage loans payable on real estate
Carrying Amount of Mortgage Notes, Related Party	0			0
Carrying Amount of Mortgage Notes, Other	$ 223,089			228,703
Effective Interest Rate (as a percent)	2.76%
Monthly Debt Service	$ 1,131
Chandler Fashion Center
Mortgage loans payable on real estate
Carrying Amount of Mortgage Notes, Related Party	0			0
Carrying Amount of Mortgage Notes, Other	$ 200,000			200,000
Effective Interest Rate (as a percent)	3.77%
Monthly Debt Service	$ 625
Danbury Fair Mall
Mortgage loans payable on real estate
Carrying Amount of Mortgage Notes, Related Party	112,018			114,265
Carrying Amount of Mortgage Notes, Other	$ 112,018			114,264
Effective Interest Rate (as a percent)	5.53%
Monthly Debt Service	$ 1,538
Deptford Mall One
Mortgage loans payable on real estate
Carrying Amount of Mortgage Notes, Related Party	0			0
Carrying Amount of Mortgage Notes, Other	$ 194,869			197,815
Effective Interest Rate (as a percent)	3.76%
Monthly Debt Service	$ 947
Deptford Mall Two
Mortgage loans payable on real estate
Carrying Amount of Mortgage Notes, Related Party	0			0
Carrying Amount of Mortgage Notes, Other	$ 14,074			14,285
Effective Interest Rate (as a percent)	6.46%
Monthly Debt Service	$ 101
Eastland Mall
Mortgage loans payable on real estate
Carrying Amount of Mortgage Notes, Related Party	0			0
Carrying Amount of Mortgage Notes, Other	$ 168,000			168,000
Effective Interest Rate (as a percent)	5.79%
Monthly Debt Service	$ 811
Fashion Outlets of Chicago
Mortgage loans payable on real estate
Carrying Amount of Mortgage Notes, Related Party	0			0
Carrying Amount of Mortgage Notes, Other	$ 200,000			$ 119,329
Effective Interest Rate (as a percent)	1.84%			2.97%
Monthly Debt Service	$ 278
Fashion Outlets of Niagara Falls USA
Mortgage loans payable on real estate
Carrying Amount of Mortgage Notes, Related Party	0			$ 0
Carrying Amount of Mortgage Notes, Other	$ 119,320			121,376
Effective Interest Rate (as a percent)	4.89%
Monthly Debt Service	$ 727
Flagstaff Mall
Mortgage loans payable on real estate
Carrying Amount of Mortgage Notes, Related Party	0			0
Carrying Amount of Mortgage Notes, Other	$ 37,000			37,000
Effective Interest Rate (as a percent)	5.03%
Monthly Debt Service	$ 153
FlatIron Crossing
Mortgage loans payable on real estate
Carrying Amount of Mortgage Notes, Related Party	0			0
Carrying Amount of Mortgage Notes, Other	$ 256,448			261,494
Effective Interest Rate (as a percent)	3.90%
Monthly Debt Service	$ 1,393
Freehold Raceway Mall
Mortgage loans payable on real estate
Carrying Amount of Mortgage Notes, Related Party	0			0
Carrying Amount of Mortgage Notes, Other	$ 226,147			229,244
Effective Interest Rate (as a percent)	4.20%
Monthly Debt Service	$ 1,132
Great Northern Mall
Mortgage loans payable on real estate
Carrying Amount of Mortgage Notes, Related Party	0			0
Carrying Amount of Mortgage Notes, Other	0			34,494
Green Acres Mall
Mortgage loans payable on real estate
Carrying Amount of Mortgage Notes, Related Party	0			0
Carrying Amount of Mortgage Notes, Other	$ 308,623			313,514
Effective Interest Rate (as a percent)	3.61%
Monthly Debt Service	$ 1,447
Kings Plaza
Mortgage loans payable on real estate
Carrying Amount of Mortgage Notes, Related Party	0			0
Carrying Amount of Mortgage Notes, Other	$ 473,205			480,761
Effective Interest Rate (as a percent)	3.67%
Monthly Debt Service	$ 2,229
Lakewood Center Mortgage
Mortgage loans payable on real estate
Carrying Amount of Mortgage Notes, Related Party	0			0
Carrying Amount of Mortgage Notes, Other	$ 408,114	$ 410,000		253,708
Effective Interest Rate (as a percent)	3.46%
Monthly Debt Service	$ 1,825
Los Cerritos Center Mortgage
Mortgage loans payable on real estate
Carrying Amount of Mortgage Notes, Related Party	99,962			103,274
Carrying Amount of Mortgage Notes, Other	$ 99,963			103,274
Effective Interest Rate (as a percent)	1.65%
Monthly Debt Service	$ 1,009
The Mall at Northgate
Mortgage loans payable on real estate
Carrying Amount of Mortgage Notes, Related Party	0			0
Carrying Amount of Mortgage Notes, Other	$ 64,000			$ 64,000
Effective Interest Rate (as a percent)	3.07%			3.05%
Monthly Debt Service	$ 130
The Oaks
Mortgage loans payable on real estate
Carrying Amount of Mortgage Notes, Related Party	0			$ 0
Carrying Amount of Mortgage Notes, Other	$ 207,055			210,197
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, Related Party	0			0
Carrying Amount of Mortgage Notes, Other	$ 131,154			133,200
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, Related Party	0			0
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, Related Party	0			0
Carrying Amount of Mortgage Notes, Other	$ 226,422			230,344
Effective Interest Rate (as a percent)	2.99%
Monthly Debt Service	$ 1,004
SanTan Village Regional Center
Mortgage loans payable on real estate
Carrying Amount of Mortgage Notes, Related Party	0			0
Carrying Amount of Mortgage Notes, Other	$ 131,636			133,807
Effective Interest Rate (as a percent)	3.14%
Monthly Debt Service	$ 589
Stonewood Center Mortgage
Mortgage loans payable on real estate
Carrying Amount of Mortgage Notes, Related Party	0			0
Carrying Amount of Mortgage Notes, Other	$ 106,963			111,297
Effective Interest Rate (as a percent)	1.80%
Monthly Debt Service	$ 640
Superstition Springs Center
Mortgage loans payable on real estate
Carrying Amount of Mortgage Notes, Related Party	0			0
Carrying Amount of Mortgage Notes, Other	$ 67,842			$ 68,079
Effective Interest Rate (as a percent)	2.03%			1.98%
Monthly Debt Service	$ 139
Towne Mall
Mortgage loans payable on real estate
Carrying Amount of Mortgage Notes, Related Party	0			$ 0
Carrying Amount of Mortgage Notes, Other	$ 22,304			22,607
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, Related Party	70,433			71,500
Carrying Amount of Mortgage Notes, Other	$ 0			0
Effective Interest Rate (as a percent)	4.23%
Monthly Debt Service	$ 368
Valley Mall
Mortgage loans payable on real estate
Carrying Amount of Mortgage Notes, Related Party	0			0
Carrying Amount of Mortgage Notes, Other	$ 40,745			41,368
Effective Interest Rate (as a percent)	5.85%
Monthly Debt Service	$ 280
Valley River Center
Mortgage loans payable on real estate
Carrying Amount of Mortgage Notes, Related Party	0			0
Carrying Amount of Mortgage Notes, Other	0			120,000
Mall of Victor Valley
Mortgage loans payable on real estate
Carrying Amount of Mortgage Notes, Related Party	0			0
Carrying Amount of Mortgage Notes, Other	$ 115,000			115,000
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, Related Party	0		$ 280,000	0
Carrying Amount of Mortgage Notes, Other	$ 277,441			0
Effective Interest Rate (as a percent)	3.55%
Monthly Debt Service	$ 1,256
Washington Square Mortgage
Mortgage loans payable on real estate
Carrying Amount of Mortgage Notes, Related Party	0			0
Carrying Amount of Mortgage Notes, Other	$ 228,095			238,696
Effective Interest Rate (as a percent)	1.65%
Monthly Debt Service	$ 1,499
Westside Pavilion
Mortgage loans payable on real estate
Carrying Amount of Mortgage Notes, Related Party	0			0
Carrying Amount of Mortgage Notes, Other	$ 147,643			$ 149,626
Effective Interest Rate (as a percent)	4.49%
Monthly Debt Service	$ 783