Annual report pursuant to Section 13 and 15(d)

Consolidated Balance Sheets (Parenthetical)

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Consolidated Balance Sheets (Parenthetical) (USD $)
In Thousands, except Share data, unless otherwise specified
Dec. 31, 2012
Dec. 31, 2011
Statement of Financial Position [Abstract]    
Accounts receivable, allowance for doubtful accounts $ 4,694 $ 3,546
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 80,952,986 72,011,324
Common Shares of beneficial interest, shares outstanding 80,952,986 72,011,324