Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 14,424	$ 12,996
Preferred shares, par (in usd per share)	$ 0.01	$ 0.01
Preferred shares, authorized (in shares)	2,000,000	2,000,000
Cumulative convertible perpetual preferred shares, dividend rate	7.25%	7.25%
Cumulative convertible perpetual preferred shares, liquidation preference (in usd per share)	$ 50	$ 50
Cumulative convertible perpetual preferred shares, issued (in shares)	1,849,000	1,849,000
Cumulative convertible perpetual preferred shares, outstanding (in shares)	1,849,000	1,849,000
Common shares of beneficial interest, par (in usd per share)	$ 0.01	$ 0.01
Common shares of beneficial interest, authorized (in shares)	240,000,000	240,000,000
Common shares of beneficial interest, issued (in shares)	83,379,000	80,055,000
Common shares of beneficial interest, outstanding (in shares)	83,379,000	80,055,000