Shareholders' Equity (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended	6 Months Ended			0 Months Ended					6 Months Ended	0 Months Ended	6 Months Ended	0 Months Ended		6 Months Ended	0 Months Ended			0 Months Ended	6 Months Ended	0 Months Ended			0 Months Ended	6 Months Ended		0 Months Ended
	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013	Jun. 06, 2014 RMR	May 08, 2014 RMR	Apr. 07, 2014 RMR	Mar. 07, 2014 RMR	Feb. 07, 2014 RMR	Jun. 30, 2014 RMR	Jul. 09, 2014 RMR Subsequent Event	Jun. 30, 2014 Equity compensation plan Officers and employees RMR	May 14, 2014 Series D	Feb. 15, 2014 Series D	Jun. 30, 2014 Series D	Jul. 25, 2014 Series D Subsequent Event	Jul. 25, 2014 Series D Subsequent Event Accrued dividend from February 15, 2014 to May 14, 2014	Jul. 25, 2014 Series D Subsequent Event Accrued dividend from May 15, 2014 to August 14, 2014	Feb. 15, 2014 Series E	Jun. 30, 2014 Series E	Jul. 25, 2014 Series E Subsequent Event	Jul. 25, 2014 Series E Subsequent Event Accrued dividend from February 15, 2014 to May 14, 2014	Jul. 25, 2014 Series E Subsequent Event Accrued dividend from May 15, 2014 to August 14, 2014	Feb. 21, 2014 Common Shares	Jun. 30, 2014 Common Shares	May 14, 2014 Common Shares	Jan. 28, 2014 Common Shares Trustees trustee	Mar. 25, 2014 Common Shares Equity compensation plan Officers and employees RMR	Jun. 30, 2014 Series D Convertible Preferred Shares
Shareholders' Equity
Common shares issued					11,729	11,275	11,410	10,625	12,187	68,206	10,980
Shares of beneficial interest granted																											2,000
Par value of shares of beneficial interest (in dollars per share)		$ 0.01		$ 0.01																							$ 0.01
Price per common share (in dollars per share)																											$ 23.46
Number of former trustees to whom common shares granted																											2
Common shares issued to holders of preferred shares													10,411,779
Preferred shares converted into common shares													10,263,003
Shares issued																												130,914
Compensation expense												$ 3.4
Cash distributions paid on preferred shares (in dollars per share)														$ 0.4063					$ 0.4531
Distribution paid or declared on preferred shares														6.2					5.0
Additional distributions on common stock declared (in dollars per share)	$ 0.25	$ 0.25	$ 0.50																					$ 0.25
Distributions paid or declared on common shares																								29.6
Distributions in arrears															3.0					7.5
Distributions in arrears (in dollars per share)															$ 0.6094					$ 0.6797
Dividend declared (in dollars per share)																$ 0.8125					$ 0.90625
Accrued dividend (in dollars per share)																	$ 0.40625	$ 0.40625				$ 0.453125	$ 0.453125
Distribution on conversion of preferred shares excess of the market value of the common shares issued above the carrying value of preferred shares															$ 16.2
Liquidation preference (in dollars per share)															$ 25.00
Percentage of average closing market price of the entity's common stock based on which ratio for conversion of preferred shares into common shares is determined															98.00%
Number of consecutive trading days considered for calculating the average of the closing sale prices of the common shares															5 days
Number of shares per $25.00 liquidation preference considered for calculating the Fundamental Change Conversion Rate																									1.0145
Common shares from conversion of preferred shares													10,263,003												2,363,969	10,411,779			4,916,997