Notes Payable (Debt Table) (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Dec. 31, 2013
Notes Payable [Line Items]
Document Fiscal Year Focus	2014
Summary of terms of notes payable
Notes payable	$ 665,852	$ 630,094
Post Oak Central Mortgage Note [Member]
Summary of terms of notes payable
Interest rate on mortgage loan	4.26%
Notes payable	186,726	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	131,900	132,714
Promenade Atlanta Mortgage Note [Member]
Summary of terms of notes payable
Interest rate on mortgage loan	4.27%
Notes payable	112,273	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	25,614	25,813
Points at Waterview mortgage note [Member]
Summary of terms of notes payable
Interest rate on mortgage loan	5.66%
Notes payable	14,872	15,139
Mahan Village LLC [Member]
Summary of terms of notes payable
Interest rate on mortgage loan	1.81%
Notes payable	14,017	14,470
Credit Facility, unsecured Member]
Summary of terms of notes payable
Interest rate on mortgage loan	1.26%
Notes payable	$ 80,450	$ 40,075