CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Preferred shares of beneficial interest, par value (in dollars per share)	$ 0.01	$ 0.01	$ 0.01
Preferred shares of beneficial interest, shares authorized (in shares)	50,000,000	50,000,000	50,000,000
Preferred shares, dividend percentage	6.50%	6.50%
Preferred shares of beneficial interest, shares issued (in shares)	4,915,196	4,915,196	4,915,196
Preferred shares, of beneficial interest, shares outstanding (in shares)	4,915,196	4,915,196	4,915,196
Preferred shares, aggregate liquidation preference	$ 122,880	$ 122,880	$ 122,880
Common shares of beneficial interest, par value (in dollars per share)	$ 0.01	$ 0.01	$ 0.01
Common shares of beneficial interest, shares authorized (in shares)	350,000,000	350,000,000	350,000,000
Common shares of beneficial interest, shares issued (in shares)	121,511,102	121,511,102	121,522,555
Common shares of beneficial interest, shares outstanding (in shares)	121,511,102	121,511,102	121,522,555