Consolidated Statements of Equity - USD ($) $ in Thousands	Preferred Stock Series J Preferred stock	Common Stock.	Accumulated Other Comprehensive Income (Loss)	Capital in Excess of Par Value	Accumulated Deficit	Common Stock Held in Treasury	Noncontrolling Interests	Total
Balance at Dec. 31, 2012	$ 44,719	$ 31	$ (90,900)	$ 9,175,724	$ (3,083,190)	$ (135,781)	$ 982,486	$ 6,893,089
Increase (Decrease) in Stockholders' Equity
Exchange of limited partner units (489,291, 70,291 and 596,051 common shares respectively in 2015, 2014 and 2013, Note 10)				11,161			(11,161)
Stock options exercised (1,567 common shares)				90				90
Series J preferred stock premium amortization	(329)							(329)
Stock incentive program (common shares, net: 63,738 in 2015, 83,509 in 2014, 107,123 in 2013)				(17,884)		17,884
Amortization of stock incentive				18,311				18,311
Issuance of unit equivalents and other, net (17, 030 common shares repurchased in 2015, 25,545 common shares issued in 2014)				346	(9,095)		50,634	41,885
Adjustment to limited partners' interest from change in ownership in the Operating Partnership, including $118,306 related to the spin-off of Washington Prime in 2014				29,615			(29,615)
Distributions to common shareholders and limited partners, excluding Operating Partnership preferred interests					(1,446,042)		(242,596)	(1,688,638)
Distribution to other noncontrolling interest partners							(285)	(285)
Other comprehensive income			15,105				2,587	17,692
Net income, excluding $1,915, $1,915 and $1,915 attributable to preferred interests in the Operating Partnership during 2015, 2014 and 2013, respectively and $8,858 attributable to noncontrolling redeemable interests in properties in 2013)					1,319,641		221,176	1,540,817
Balance at Dec. 31, 2013	44,390	31	(75,795)	9,217,363	(3,218,686)	(117,897)	973,226	6,822,632
Increase (Decrease) in Stockholders' Equity
Exchange of limited partner units (489,291, 70,291 and 596,051 common shares respectively in 2015, 2014 and 2013, Note 10)				1,297			(1,297)
Issuance of limited partner units							84,910	84,910
Series J preferred stock premium amortization	(328)							(328)
Stock incentive program (common shares, net: 63,738 in 2015, 83,509 in 2014, 107,123 in 2013)				(14,026)		14,026
Redemption of limited partner units				(12,972)			(1,463)	(14,435)
Amortization of stock incentive				18,256				18,256
Spin-off of Washington Prime					(812,763)			(812,763)
Long-term incentive performance units							49,938	49,938
Issuance of unit equivalents and other, net (17, 030 common shares repurchased in 2015, 25,545 common shares issued in 2014)				662	18,281	(58)	12,081	30,966
Adjustment to limited partners' interest from change in ownership in the Operating Partnership, including $118,306 related to the spin-off of Washington Prime in 2014				211,657			(211,657)
Distributions to common shareholders and limited partners, excluding Operating Partnership preferred interests					(1,603,603)		(271,640)	(1,875,243)
Distribution to other noncontrolling interest partners							(19,065)	(19,065)
Other comprehensive income			14,754				2,272	17,026
Net income, excluding $1,915, $1,915 and $1,915 attributable to preferred interests in the Operating Partnership during 2015, 2014 and 2013, respectively and $8,858 attributable to noncontrolling redeemable interests in properties in 2013)					1,408,588		241,023	1,649,611
Balance at Dec. 31, 2014	44,062	31	(61,041)	9,422,237	(4,208,183)	(103,929)	858,328	5,951,505
Increase (Decrease) in Stockholders' Equity
Exchange of limited partner units (489,291, 70,291 and 596,051 common shares respectively in 2015, 2014 and 2013, Note 10)				7,942			(7,942)
Series J preferred stock premium amortization	(329)							(329)
Stock incentive program (common shares, net: 63,738 in 2015, 83,509 in 2014, 107,123 in 2013)				(13,103)		13,103
Redemption of limited partner units				(147,841)			(14,843)	(162,684)
Amortization of stock incentive				13,692				13,692
Treasury stock purchase (1,903,340 shares in 2015)						(343,007)		(343,007)
Long-term incentive performance units							47,279	47,279
Issuance of unit equivalents and other, net (17, 030 common shares repurchased in 2015, 25,545 common shares issued in 2014)				43	(7,285)	(3,301)	4,537	(6,006)
Adjustment to limited partners' interest from change in ownership in the Operating Partnership, including $118,306 related to the spin-off of Washington Prime in 2014				101,480			(101,480)
Distributions to common shareholders and limited partners, excluding Operating Partnership preferred interests					(1,879,182)		(314,944)	(2,194,126)
Distribution to other noncontrolling interest partners							(3,836)	(3,836)
Other comprehensive income			(191,645)				(31,934)	(223,579)
Net income, excluding $1,915, $1,915 and $1,915 attributable to preferred interests in the Operating Partnership during 2015, 2014 and 2013, respectively and $8,858 attributable to noncontrolling redeemable interests in properties in 2013)					1,827,720		309,740	2,137,460
Balance at Dec. 31, 2015	$ 43,733	$ 31	$ (252,686)	$ 9,384,450	$ (4,266,930)	$ (437,134)	$ 744,905	$ 5,216,369