Investment in Unconsolidated Joint Ventures (Ten Peachtree Place Associates) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended			1 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	May 31, 2012
Schedule of Equity Method Investments [Line Items]
Proceeds from investment property sales	$ 244,471	$ 178,966	$ 273,386
Ten Peachtree Place Associates [Member]
Schedule of Equity Method Investments [Line Items]
Proceeds from investment property sales				45,300
Company's share of gain on sale of equity investee property				$ 7,300
Midtown Atlanta Georgia [Member] | Ten Peachtree Place Associates [Member]
Schedule of Equity Method Investments [Line Items]
Square footage of real estate property (square feet)			260,000
Wholly Owned Subsidiary of Coca Cola Company [Member] | Ten Peachtree Place Associates [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage of Partner in Joint Venture			50.00%