Noncontrolling Interests on the Company's Consolidated Financial Statements (Details) (USD $)	12 Months Ended
	Dec. 31, 2012 D	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Series A Cummulative Redeemable Preferred Unit [Member]	Aug. 15, 2012 Series A Cummulative Redeemable Preferred Unit [Member]
Temporary Equity [Line Items]
7.45% Series A cumulative redeemable preferred units of the Operating Partnership outstanding					1,500,000
Preferred units redemption value per unit					$ 50
Redemption value					$ 75,000,000
Preferred stock redemption premium	6,980,000	0	0	2,100,000
Accrued distribution payable	700,000
Noncontrolling Interest (Textuals) [Abstract]
Percentage of general partnership interest owned by the company in the Operating Partnership	97.60%	97.20%
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%	2.80%
Noncontrolling common units	1,826,503	1,718,131
Issuance of common units in connection with an operating property acquisition	118,372
Common stock, par value	$ 0.01	$ 0.01
Number of trading days	10
Aggregate value upon redemption of outstanding noncontrolling common units	$ 85,400,000	$ 64,700,000