Discontinued Operations (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended	3 Months Ended	9 Months Ended										3 Months Ended	12 Months Ended		3 Months Ended	12 Months Ended		3 Months Ended	12 Months Ended				3 Months Ended	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Sep. 30, 2013 Portfolio sale 3 malls and 3 associated centers [Member] Properties	Sep. 30, 2013 Georgia Square and Georgia Square Plaza [Member]		Sep. 30, 2013 1500 Sunday Drive [Member]	Sep. 30, 2013 Peninsula Business Center I and II [Member]	Sep. 30, 2013 Lake Point and SunTrust Office [Member]		Sep. 30, 2013 706 and 708 Green Valley Road [Member]		Sep. 30, 2013 Various [Member]		Sep. 30, 2012 Willowbrook Plaza [Member]	Dec. 31, 2012 Willowbrook Plaza [Member]		Sep. 30, 2012 Towne Mall [Member]	Dec. 31, 2012 Towne Mall [Member]		Sep. 30, 2012 Hickory Hollow Mall [Member]	Dec. 31, 2012 Hickory Hollow Mall [Member]		Dec. 31, 2012 Massard Crossing [Member]	Dec. 31, 2012 Settlers Ridge Phase II [Member]	Mar. 31, 2012 Oak Hollow Square [Member]	Dec. 31, 2012 Oak Hollow Square [Member]		Dec. 31, 2012 Westridge Square [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sales of Real Estate			$ 220,425		$ 67,594		$ 176,000	[1]	$ 8,300	$ 5,250	$ 30,875	[2]						$ 24,450	[3]		$ 950	[4]		$ 1,000	[5]	$ 7,803	$ 19,144		$ 14,247	[6]
Impairment of Long-Lived Assets to be Disposed of						5,234											17,743			419			8,047					255
Properties Sold						6
Gain on discontinued operations	290	88	1,162	983	983				(549)	598	823	[2]	281	[7]	9	[8]		0	[3]		0	[4]		0	[5]	98	858		(1)	[6]	28	[8]
Proceeds from Sale of Real Estate			215,450		66,208		171,977	[1]	7,862	5,121	30,490	[2]						24,171	[3]		892	[4]		966	[5]	7,432	18,951		13,796	[6]
Revenues of discontinued operations	1,932	10,656	16,163	33,925
Assets of Disposal Group, Including Discontinued Operation	$ 219,829		$ 219,829

[1] Net loss on impairment of $5,234 recorded in the third quarter of 2013 to write down the book value of six properties sold in a portfolio sale to the net sales price.

[2] Classified as held for sale as of December 31, 2012.

[3] Loss on impairment of $17,743 recorded in the third quarter of 2012 to write down the book value of this property to its then estimated fair value.

[4] Loss on impairment of $419 recorded in the third quarter of 2012 to write down the book value of this property to expected sales price.

[5] Loss on impairment of $8,047 recorded in the third quarter of 2012 to write down the book value of this property to expected sales price.

[6] Loss on impairment of $255 recorded in the first quarter of 2012 related to the true-up of certain estimated amounts to actual amounts.

[7] Recognition of gain deferred in December 2008 until subsequent repayment of notes receivable.

[8] Reflects subsequent true-ups for settlement of estimated expenses based on actual amounts.