Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data	Sep. 30, 2011	Dec. 31, 2010
Consolidated Balance Sheets
Accounts receivable, allowance for doubtful accounts (in dollars)	$ 3,404	$ 2,796
Preferred Shares of beneficial interest, aggregate liquidation preference (in dollars)	$ 216,333	$ 216,333
Preferred Shares of beneficial interest, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred Shares of beneficial interest, shares authorized	15,000,000	15,000,000
Preferred Shares of beneficial interest, shares issued	8,121,667	8,121,667
Preferred Shares of beneficial interest, shares outstanding	8,121,667	8,121,667
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	71,986,936	66,931,582
Common Shares of beneficial interest, shares outstanding	71,986,936	66,931,582