Notes Payable, Commitments and Contingencies (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Summary of terms of notes payable
Debt instrument description of variable rate basis, LIBOR	the spread over LIBOR was 2.0%
Debt instrument, basis spread on variable rate minimum	2.00%
Notes payable	$ 539,442	$ 509,509
Credit Facility, unsecured [Member]
Summary of terms of notes payable
Debt instrument description of variable rate basis, LIBOR	LIBOR
Debt instrument, Term	5 years
Maturity date of debt instrument	Aug. 29, 2012
Notes payable	198,250	105,400
Terminus 100 mortgage note [Member]
Summary of terms of notes payable
Interest rate on mortgage loan	5.25%
Debt instrument, Term	12 years
Debt instrument, amortization period	30 years
Maturity date of debt instrument	Jan. 01, 2023
Notes payable	138,194	140,000
The American Cancer Society Center mortgage note [Member]
Summary of terms of notes payable
Interest rate on mortgage loan	6.45%
Debt instrument, Term	10 years
Debt instrument, amortization period	30 years
Maturity date of debt instrument	Sep. 01, 2017
Notes payable	135,650	136,000
Meridian Mark Plaza mortgage note [Member]
Summary of terms of notes payable
Interest rate on mortgage loan	6.00%
Debt instrument, Term	10 years
Debt instrument, amortization period	30 years
Maturity date of debt instrument	Aug. 01, 2020
Notes payable	26,554	26,892
100/200 North Point Center East mortgage note [Member]
Summary of terms of notes payable
Interest rate on mortgage loan	5.39%
Debt instrument, Term	5 years
Debt instrument, amortization period	30 years
Maturity date of debt instrument	Jun. 01, 2012
Notes payable	24,478	24,830
Points at Waterview mortgage note [Member]
Summary of terms of notes payable
Interest rate on mortgage loan	5.66%
Debt instrument, Term	10 years
Debt instrument, amortization period	25 years
Maturity date of debt instrument	Jan. 01, 2016
Notes payable	16,135	16,592
Callaway Gardens [Member]
Summary of terms of notes payable
Interest rate on mortgage loan	4.13%
Maturity date of debt instrument	Nov. 18, 2013
Notes payable	180	173
Mahan Village LLC [Member]
Summary of terms of notes payable
Interest rate on mortgage loan	3.25%
Debt instrument, Term	3 years
Maturity date of debt instrument	Sep. 12, 2014
Notes payable	1	0
333/555 North Point Center East mortgage note [Member]
Summary of terms of notes payable
Interest rate on mortgage loan	7.00%
Debt instrument, Term	10 years
Debt instrument, amortization period	25 years
Maturity date of debt instrument	Nov. 01, 2011
Notes payable	0	26,412
Lakeshore Park Plaza mortgage note [Member]
Summary of terms of notes payable
Interest rate on mortgage loan	5.89%
Debt instrument, Term	4 years
Debt instrument, amortization period	25 years
Maturity date of debt instrument	Aug. 01, 2012
Notes payable	0	17,544
600 University Park Place mortgage note [Member]
Summary of terms of notes payable
Interest rate on mortgage loan	7.38%
Debt instrument, Term	10 years
Debt instrument, amortization period	30 years
Maturity date of debt instrument	Aug. 10, 2011
Notes payable	0	12,292
Handy Road Associates, LLC [Member]
Summary of terms of notes payable
Debt instrument description of variable rate basis, LIBOR	Prime
Debt instrument, basis spread on variable rate minimum	1.00%
Debt instrument, Term	5 years
Debt instrument, interest rate, Minimum	6.00%
Maturity date of debt instrument	Mar. 30, 2011
Notes payable	$ 0	$ 3,374