Investment in Unconsolidated Joint Ventures (Ten Peachtree Place Associates) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended			1 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	May 31, 2012 Ten Peachtree Place Associates [Member]	Dec. 31, 2012 Ten Peachtree Place Associates [Member]	Dec. 31, 2012 Wholly Owned Subsidiary of Coca Cola Company [Member] Ten Peachtree Place Associates [Member]	Dec. 31, 2012 Midtown Atlanta Georgia [Member] Ten Peachtree Place Associates [Member] sqft
Schedule of Equity Method Investments [Line Items]
Ownership Percentage of partner joint venture (percent)						50.00%
Square footage of real estate property (square feet)							260,000
Proceeds from investment property sales	$ 273,386	$ 143,623	$ 101,706	$ 45,300
Company's share of gain on sale of equity investee property				$ 7,300	$ 7,300