Dispositions: (Details) $ in Thousands											9 Months Ended
	Jun. 30, 2015 USD ($) ft²	Dec. 29, 2014 USD ($) ft²	Oct. 31, 2014 USD ($) ft²	Oct. 10, 2014 USD ($)	Sep. 11, 2014 USD ($)	Aug. 28, 2014 USD ($)	Jul. 07, 2014 USD ($)	Mar. 17, 2014 USD ($) ft² note	Feb. 14, 2014 USD ($) ft²	Jan. 15, 2014 USD ($) ft²	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)
Discontinued Operations:
(Gain) loss on extinguishment of debt, net											$ (609)	$ 405
Camelback Colonnade
Discontinued Operations:
Property area (in square feet) | ft²		619,000
Proceeds from sale		$ 92,898
Gain (loss) from sale		$ 24,554
Percentage of loan assumed by third party (as a percent)		67.50%
Cash payment		$ 61,173
Assumption of debt		31,725
Notes payable discharged		47,946
Noncontrolling interest adjustment		$ 17,217
Great Northern Mall
Discontinued Operations:
(Gain) loss on extinguishment of debt, net	$ 1,627
Rotterdam Square
Discontinued Operations:
Property area (in square feet) | ft²										585,000
Proceeds from sale										$ 8,500
Gain (loss) from sale										$ (472)
Somersville Town Center
Discontinued Operations:
Property area (in square feet) | ft²									348,000
Proceeds from sale									$ 12,337
Gain (loss) from sale									$ (263)
Lake Square Mall
Discontinued Operations:
Property area (in square feet) | ft²								559,000
Proceeds from sale								$ 13,280
Gain (loss) from sale								(876)
Cash payment								$ 3,677
Lake Square Mall | Notes Receivable
Discontinued Operations:
Number of notes receivable (in notes) | note								2
Notes receivable								$ 9,603
Mervyn's
Discontinued Operations:
Proceeds from sale				$ 1,900	$ 1,200	$ 3,500	$ 3,560
Gain (loss) from sale				$ (3)	$ 315	$ (80)	$ (158)
South Towne Center
Discontinued Operations:
Property area (in square feet) | ft²			1,278,000
Proceeds from sale			$ 205,000
Gain (loss) from sale			$ 121,873
Great Northern Mall | Great Northern Mall
Discontinued Operations:
Property area (in square feet) | ft²	895,000
(Gain) loss on extinguishment of debt, net	$ 1,627