Quarterly report pursuant to Section 13 or 15(d)

Consolidated Balance Sheets (Parenthetical)

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Consolidated Balance Sheets (Parenthetical) (USD $)
In Thousands, except Share data, unless otherwise specified
Mar. 31, 2013
Dec. 31, 2012
Statement of Financial Position [Abstract]    
Accounts receivable, allowance for doubtful accounts $ 5,351 $ 4,694
Preferred Shares of beneficial interest, par value (in dollars per share) $ 0.01 $ 0.01
Preferred Shares of beneficial interest, shares authorized 25,000,000 25,000,000
Preferred Shares of beneficial interest, shares issued 12,821,667 12,821,667
Preferred Shares of beneficial interest, shares outstanding 12,821,667 12,821,667
Common Shares of beneficial interest, par value (in dollars per share) $ 0.01 $ 0.01
Common Shares of beneficial interest, shares authorized 125,000,000 125,000,000
Common Shares of beneficial interest, shares issued 85,758,438 80,952,986
Common Shares of beneficial interest, shares outstanding 85,758,438 80,952,986