Real Estate and Accumulated Depreciation (Schedule of Properties) (Details) (USD $) In Thousands, unless otherwise specified									12 Months Ended																						12 Months Ended					12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2013 Operating Properties Office [Member]	Dec. 31, 2013 Operating properties	Dec. 31, 2013 Impairment moved to discontinued operations	Dec. 31, 2013 Commercial Real Estate [Member] Impairment moved to discontinued operations	Dec. 31, 2013 Residential Lots [Member] Impairment moved to discontinued operations	Dec. 31, 2013 Greenway Plaza Houston, TX [Member] Operating Properties Office [Member]	Dec. 31, 2013 One Ninety One Peachtree Tower Atlanta [Member] Operating Properties Office [Member]	Dec. 31, 2013 Terminus 100 Atlanta, GA [Member] Operating Properties Office [Member]	Dec. 31, 2013 777 Main Fort Worth, TX [Member] Operating Properties Office [Member]	Dec. 31, 2013 Promenade Atlanta, GA [Member] Operating Properties Office [Member]	Dec. 31, 2013 The American Cancer Society Center Atlanta, GA [Member] Operating Properties Office [Member]	Dec. 31, 2013 816 Congress Austin, TX [Member] Operating Properties Office [Member]	Dec. 31, 2013 2100 Ross Avenue [Member] Operating Properties Office [Member]	Dec. 31, 2013 The Points at Waterview Suburban Dallas, TX [Member] Operating Properties Office [Member]	Dec. 31, 2013 Meridian Mark Plaza Atlanta, GA [Member] Operating Properties Office [Member]	Dec. 31, 2013 555 North Point Center East Suburban Atlanta, GA [Member] Operating Properties Office [Member]	Dec. 31, 2013 221 Peachtree Center Avenue Parking Garage Atlanta, GA [Member] Operating Properties Office [Member]	Dec. 31, 2013 333 North Point Center East Suburban Atlanta, GA [Member] Operating Properties Office [Member]	Dec. 31, 2013 100 North Point Center East Suburban Atlanta, GA [Member] Operating Properties Office [Member]	Dec. 31, 2013 200 North Point Center East Suburban Atlanta, GA [Member] Operating Properties Office [Member]	Dec. 31, 2013 Mahan Village Tallahassee FL [Member] Operating Properties Retail [Member]	Dec. 31, 2013 Round Rock Land Austin, TX [Member] Commercial Real Estate [Member] Impairment moved to discontinued operations	Dec. 31, 2013 Research Park Austin [Member] Commercial Real Estate [Member] Impairment moved to discontinued operations	Dec. 31, 2013 Land Adjacent to The Avenue Forsyth Suburban Atlanta [Member] Commercial Real Estate [Member] Impairment moved to discontinued operations	Dec. 31, 2013 Blalock Lakes Suburban Atlanta, GA [Member] Commercial Real Estate [Member] Impairment moved to discontinued operations	Dec. 31, 2013 Blalock Lakes Suburban Atlanta, GA [Member] Residential Lots [Member] Impairment moved to discontinued operations	Dec. 31, 2013 549 / 555 / 557 Peachtree Street Atlanta, GA [Member] Commercial Real Estate [Member] Impairment moved to discontinued operations	Dec. 31, 2013 North Point Suburban Atlanta, GA [Member] Commercial Real Estate [Member] Impairment moved to discontinued operations	Dec. 31, 2013 Wildwood Suburban Atlanta, GA [Member] Commercial Real Estate [Member] Impairment moved to discontinued operations	Dec. 31, 2013 Callaway Gardens Pine Mountain, GA [Member] Residential Lots [Member] Impairment moved to discontinued operations	Dec. 31, 2013 Assets Held-for-sale [Member]	Dec. 31, 2013 Assets Held-for-sale [Member] Lakeshore Park Plaza Birmingham, AL [Member]	Dec. 31, 2013 Assets Held-for-sale [Member] 600 University Park Place Birmingham, AL [Member]	Dec. 31, 2013 Operating Properties [Member]
Real Estate and Accumulated Depreciation
Encumbrances					$ 575,549	$ 590,019	$ 0	$ 0	$ 0	$ 0	$ 100,000	$ 188,310	$ 0	$ 113,573	$ 132,714	$ 0	$ 0	$ 15,139	$ 25,813	$ 0	$ 0	$ 0	$ 0	$ 0	$ 14,470	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 590,019
Initial cost to company, land and improvements					444,907	450,284	83,798	64,557	19,241	273,651	5,355	87,264	32,872	13,439	5,226	6,817	5,987	2,558	2,219	368	4,217	551	1,475	1,726	5,377	12,802	4,373	11,240	9,646	17,657	5,988	10,294	10,214	1,584	5,261	3,362	1,899	534,082
Initial cost to company, building and improvements					1,330,311	1,330,311	0	0	0	595,547	141,012	129,347	104,823	102,790	67,370	89,891	45,739	22,910	0	0	13,337	0	9,625	7,920	0	0	0	0	0	0	0	0	0	0	12,261	12,261	0	1,330,311
Costs capitalized subsequent to acquisition, land and improvements					2,185	2,185	(48,745)	(39,664)	(9,081)	0	0	0	0	0	0	3,282	0	85	0	0	0	0	0	0	0	(5,063)	653	(7,540)	(6,301)	(12,084)	(3,363)	(8,851)	(9,199)	3,003	0	0	0	(46,560)
Costs capitalized subsequent to acquisition, building and improvements					261,001	281,364	0	0	0	5,116	87,704	13,600	4,082	24,252	30,179	2,710	15,732	8,361	26,858	21,920	348	14,984	2,539	2,616	20,363	0	0	0	0	0	0	0	0	0	26,415	6,735	19,680	303,045
Gross amount at which carried at close of period, land and improvements					447,092	452,469	35,053	24,893	10,160	273,651	5,355	87,264	32,872	13,439	5,226	10,099	5,987	2,643	2,219	368	4,217	551	1,475	1,726	5,377	7,739	5,026	3,700	3,345	5,573	2,625	1,443	1,015	4,587	5,261	3,362	1,899	487,522
Gross amount at which carried at close of period, building and Improvements less cost of sales, transfers and other					1,591,312	1,611,675	0	0	0	600,663	228,716	142,947	108,905	127,042	97,549	92,601	61,471	31,271	26,858	21,920	13,685	14,984	12,164	10,536	20,363	0	0	0	0	0	0	0	0	0	38,676	18,996	19,680	1,633,356
Gross amount at which carried at close of period, total	2,164,815	997,323	1,253,414	1,363,320	2,038,404	2,064,144	35,053	24,893	10,160	874,314	234,071	230,211	141,777	140,481	102,775	102,700	67,458	33,914	29,077	22,288	17,902	15,535	13,639	12,262	25,740	7,739	5,026	3,700	3,345	5,573	2,625	1,443	1,015	4,587	43,937	22,358	21,579	2,120,878
Accumulated depreciation	$ 257,151	$ 258,258	$ 289,473	$ 274,925	$ 234,674	$ 235,707	$ 0	$ 0	$ 0	$ 10,791	$ 65,995	$ 6,491	$ 2,329	$ 11,781	$ 59,402	$ 2,392	$ 5,274	$ 18,314	$ 15,736	$ 12,171	$ 2,377	$ 9,332	$ 6,810	$ 5,479	$ 1,033	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 21,444	$ 12,001	$ 9,443	$ 235,707
Life on which depreciation in statement of operations is computed (b)									0 years	30 years	40 years	42 years	24 years	34 years	25 years	42 years	35 years	25 years	30 years	30 years	39 years	30 years	25 years	25 years	30 years	0 years	0 years	0 years	0 years		0 years	0 years	0 years	0 years		30 years	30 years