Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2014	Dec. 31, 2013
Accounts receivable, allowance for doubtful accounts	$ 2,217	$ 2,351
Preferred shares, par (in shares)	$ 0.01	$ 0.01
Common shares of beneficial interest, par (in usd per share)	$ 0.01	$ 0.01
Common shares of beneficial interest, shares authorized (in shares)	120,000,000	120,000,000
Common shares of beneficial interest, shares issued (in shares)	69,937,000	66,669,000
Common shares of beneficial interest, shares outstanding (in shares)	69,937,000	66,669,000
Series D Preferred Stock
Preferred shares, shares authorized (in shares)	2,000,000	2,000,000
Cumulative Perpetual Convertible Preferred Shares, shares issued (in shares)	2,000,000	2,000,000
Cumulative Perpetual Convertible Preferred Shares, shares outstanding (in shares)	2,000,000	2,000,000
Cumulative Perpetual Convertible Preferred Shares, liquidation preference (in usd per share)	$ 50	$ 50
Cumulative Perpetual Convertible Preferred Shares, dividend rate percentage	7.25%	7.25%