Noncontrolling Interests on the Company's Consolidated Financial Statements (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013 NumberofTradingDays	Dec. 31, 2012	Mar. 31, 2012
Noncontrolling Interest (Textuals) [Abstract]
Percentage of general partnership interest owned by the company in the Operating Partnership	97.60%	97.60%	97.50%
Percentage of Common limited partnership interest owned by certain non-affiliated investors and certain directors and officers of the Company in the Operating Partnership	2.40%	2.40%	2.50%
Common units outstanding held by common limited partners	1,826,503	1,826,503	1,718,131
Conversion ratio of common units for common stock	1.0
Common stock, par value	$ 0.01	$ 0.01	$ 0.01
Number of trading days	10
Aggregate value upon redemption of outstanding noncontrolling common units	$ 95.9	$ 85.4