Notes Payable (Other Debt Information Textuals) (Details) (USD $)			12 Months Ended				12 Months Ended		12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013 Long Term Debt Nonrecourse	Dec. 31, 2013 Line of Credit [Member]	Dec. 31, 2013 Post Oak Central Mortgage Note [Member] sqft	Sep. 06, 2013 Post Oak Central Mortgage Note [Member]	Dec. 31, 2013 Promenade Atlanta Mortgage Note [Member] sqft	Sep. 06, 2013 Promenade Atlanta Mortgage Note [Member]	Dec. 31, 2013 191 Peachtree Tower mortgage note	Dec. 31, 2012 191 Peachtree Tower mortgage note sqft	Feb. 28, 2013 Terminus Office Holdings [Member]	Dec. 31, 2013 Institutional investors advised by J.P. Morgan Asset Management [Member] Terminus Office Holdings [Member]
Debt Instrument [Line Items]
Debt instrument original principal amount					$ 189,000,000		$ 114,000,000			$ 100,000,000	$ 82,000,000
Square footage of real estate property (square feet)					1,300,000		800,000			1,200,000
Interest rate on mortgage loan (percent)				1.67%	4.26%	4.26%	4.27%	4.27%	3.35%
Debt Instrument, Date of First Required Payment									May 01, 2016
Debt Instrument, Maturity Date				Feb. 28, 2016	Oct. 01, 2020		Oct. 01, 2022		Oct. 01, 2018
Equity Method Investment, Ownership Percentage											50.00%	50.00%
Carrying value of assets pledged as collateral for debt			592,800,000
Mortgage Notes Payable	575,500,000
Weighted average maturity of consolidated debt			5 years 7 months
Notes Payable, Fair Value Disclosure	$ 654,100,000	$ 456,000,000