Notes Payable (Debt Table) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Sep. 06, 2013
Summary of terms of notes payable
Notes payable	$ 587,442	$ 630,094
Post Oak Central Mortgage Note [Member]
Summary of terms of notes payable
Interest rate on mortgage loan			4.26%
Notes payable	187,522	188,310
The American Cancer Society Center mortgage note [Member]
Summary of terms of notes payable
Interest rate on mortgage loan	6.45%
Notes payable	132,287	132,714
Promenade Atlanta Mortgage Note [Member]
Summary of terms of notes payable
Interest rate on mortgage loan			4.27%
Notes payable	112,927	113,573
191 Peachtree Tower Mortgage Note [Member]
Summary of terms of notes payable
Interest rate on mortgage loan	3.35%
Notes payable	100,000	100,000
Meridian Mark Plaza mortgage note [Member]
Summary of terms of notes payable
Interest rate on mortgage loan	6.00%
Notes payable	25,714	25,813
Points at Waterview mortgage note [Member]
Summary of terms of notes payable
Interest rate on mortgage loan	5.66%
Notes payable	15,007	15,139
Mahan Village LLC [Member]
Summary of terms of notes payable
Interest rate on mortgage loan	1.80%
Notes payable	13,985	14,470
Credit Facility, unsecured Member]
Summary of terms of notes payable
Interest rate on mortgage loan	1.65%
Notes payable	$ 0	$ 40,075