Notes Payable (Debt Table) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013 Terminus 100 mortgage note	Sep. 06, 2013 Terminus 100 mortgage note	Dec. 31, 2012 Terminus 100 mortgage note	Dec. 31, 2013 The American Cancer Society Center mortgage note	Dec. 31, 2012 The American Cancer Society Center mortgage note	Dec. 31, 2013 Promenade Atlanta Mortgage Note [Member]	Sep. 06, 2013 Promenade Atlanta Mortgage Note [Member]	Dec. 31, 2012 Promenade Atlanta Mortgage Note [Member]	Dec. 31, 2013 191 Peachtree Tower mortgage note	Dec. 31, 2012 191 Peachtree Tower mortgage note	Dec. 31, 2013 Credit Facility, unsecured	Dec. 31, 2012 Credit Facility, unsecured	Dec. 31, 2013 Meridian Mark Plaza mortgage note	Dec. 31, 2012 Meridian Mark Plaza mortgage note	Dec. 31, 2013 The Points at Waterview mortgage note	Dec. 31, 2012 The Points at Waterview mortgage note	Dec. 31, 2013 Mahan Village LLC contruction facility	Dec. 31, 2012 Mahan Village LLC contruction facility	Dec. 31, 2013 Terminus One Hundred Mortgage Note [Member]	Dec. 31, 2012 Terminus One Hundred Mortgage Note [Member]	Dec. 31, 2013 Callaway Gardens mortgage note	Dec. 31, 2012 Callaway Gardens mortgage note
Debt Instrument [Line Items]
Document Fiscal Year Focus	2013
Interest Rate (percent)			4.26%	4.26%		6.45%		4.27%	4.27%		3.35%		1.67%		6.00%		5.66%				5.25%		4.13%
Notes Payable	$ 630,094	$ 425,410	$ 188,310		$ 0	$ 132,714	$ 134,243	$ 113,573		$ 0	$ 100,000	$ 100,000	$ 40,075	$ 0	$ 25,813	$ 26,194	$ 15,139	$ 15,651	$ 14,470	$ 13,027	$ 0	$ 136,123	$ 0	$ 172