Dispositions: (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended			0 Months Ended													1 Months Ended	0 Months Ended					1 Months Ended	0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Sep. 30, 2009	Dec. 11, 2013	Dec. 29, 2014	Oct. 10, 2014	Sep. 11, 2014	Aug. 28, 2014	Jul. 07, 2014	Dec. 04, 2013	Oct. 23, 2013	Oct. 15, 2013	Sep. 11, 2013	May 11, 2012	Apr. 23, 2012	Mar. 31, 2012	Apr. 30, 2012 sqft	May 17, 2012 sqft	May 31, 2012 sqft	Jun. 28, 2012 sqft	Sep. 30, 2013	Dec. 31, 2012 sqft	May 31, 2013 sqft	Jun. 04, 2013	Jan. 15, 2014 sqft	Feb. 14, 2014	Mar. 17, 2014	Oct. 31, 2014	Sep. 17, 2013 sqft	Dec. 31, 2011 sqft
Discontinued Operations:
Gain (loss) from sale	$ 0	$ 286,414	$ 50,811
Gain (loss) on extinguishment of debt	(526)	1,432	0
Revenues from discontinued operations		54,752	94,406
Gain (loss) income from discontinued operations	0	289,936	63,223
Freehold Raceway Mall and Chandler Fashion Center
Discontinued Operations:
Ownership interest (as a percent)				49.90%
Chesterfield Towne Center
Discontinued Operations:
Gain (loss) from sale					151,467
Camelback Colonnade
Discontinued Operations:
Proceeds from sale						92,898
Gain (loss) from sale						24,554
Property square footage																														619,000
Cash payment						61,173
Assumption of debt						31,725
Debt discharged						47,946
Noncontrollling interest adjustment						17,217
Camelback Colonnade | Freehold Raceway Mall and Chandler Fashion Center
Discontinued Operations:
Ownership interest (as a percent)						67.50%
Mervyn's
Discontinued Operations:
Proceeds from sale							1,900	1,200	3,500	3,560	10,475	5,430	5,700	12,000	20,750
Gain (loss) from sale							(3)	315	(80)	(158)	(5,257)	1,695	(2,031)	(2,633)	(407)
Valley View Mall
Discontinued Operations:
Impairment charge																	54,306
Long-lived assets written off to fair value																33,450
Gain (loss) on extinguishment of debt																104,023
The Borgata
Discontinued Operations:
Proceeds from sale																		9,150
Gain (loss) from sale																		(1,275)
Property square footage																		94,000
Hilton Village
Discontinued Operations:
Proceeds from sale																			24,820
Gain (loss) from sale																			3,127
Property square footage																			80,000
Prescott Gateway
Discontinued Operations:
Property square footage																				584,000
Gain (loss) on extinguishment of debt																				16,296
Carmel Plaza
Discontinued Operations:
Proceeds from sale																					52,000
Gain (loss) from sale																					7,844
Property square footage																					112,000
Fiesta Mall
Discontinued Operations:
Impairment charge																							24,555
Property square footage			933,000																				933,000
Gain (loss) on extinguishment of debt																						1,252
Green Tree Mall
Discontinued Operations:
Proceeds from sale																								79,000
Gain (loss) from sale																								59,767
Property square footage																								793,000
Northridge Mall
Discontinued Operations:
Property square footage																									890,000
Rimrock Mall
Discontinued Operations:
Property square footage																									603,000
Rimrock Mall and Nortridge Mall
Discontinued Operations:
Proceeds from sale																									230,000
Gain (loss) from sale																									82,151
Chesterfield Towne Center
Discontinued Operations:
Property square footage					1,016,000
Cash payment					67,763
Assumption of debt					109,737
Centre at Salisbury
Discontinued Operations:
Proceeds from sale					292,500
Property square footage					862,000
Assumption of debt					115,000
Rotterdam Square
Discontinued Operations:
Proceeds from sale																										8,500
Gain (loss) from sale																										(435)
Property square footage																										585,000
Somersville Town Center
Discontinued Operations:
Proceeds from sale																											12,337
Gain (loss) from sale																											(263)
Property square footage	348,000
Lake Square Mall
Discontinued Operations:
Proceeds from sale																												13,280
Gain (loss) from sale																												(876)
Property square footage																															559,000
Cash payment																												3,677
South Towne Center
Discontinued Operations:
Proceeds from sale																													205,000
Gain (loss) from sale																													121,873
Property square footage																													1,278,000
Notes Receivable | Lake Square Mall
Discontinued Operations:
Notes receivable																												$ 9,603
Number of notes receivable																												2