Related Person Transactions - Management Agreements with RMR LLC (Details)				12 Months Ended
	Dec. 23, 2015 installment	Jun. 05, 2015 agreement	May. 09, 2014 factor	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($) $ / shares	Dec. 23, 2013 USD ($)
Related Party Transaction [Line Items]
Rental income				$ 283,115,000	$ 258,062,000	$ 251,866,000
Travel Centers of America LLC
Related Party Transaction [Line Items]
Rental income				250,582,000	$ 225,394,000	219,050,000
RMR LLC
Related Party Transaction [Line Items]
Base management fee payable as a percentage of aggregate book value of real estate assets or transferred assets						$ 0.5
Base management fee payable as a percentage of average historical cost of real estate investments, excluding transferred assets for investments up to specified amount						0.70%
Threshold amount of other real estate investments for payment of base management fee						$ 250,000,000
Annual business management fee as a percentage of aggregate cost of properties acquired in excess of $250,000						0.50%
Incentive fee as a percentage of the product of weighted average common shares outstanding on a fully diluted basis and the excess, if any of the Normalized FFO Per Share for current fiscal year over the preceding fiscal year						15.00%
Cap on the value of incentive fee (USD per shares) | $ / shares						$ 0.02
Rental income				$ 33,000
Property management fees as a percentage of gross collected rents				3.00%
Construction supervision fees as a percentage of construction costs				5.00%
Termination Fee Factor			2.75
Number consecutive months for average fees and expenses			24 months
Termination of property management agreement in relation to business management agreement termination			12 months
Termination fee factor property management fee | factor			12
Number of months used to calculate property management termination fee			6 months
Period over which transition services will be provided by the related party after termination of the agreement			120 days
RMR LLC | Amended Agreement
Related Party Transaction [Line Items]
Base management fee payable as a percentage of average historical cost of real estate investments, excluding transferred assets for investments up to specified amount							0.70%
Base management fee payable as a percentage of average historical cost of real estate investments, excluding transferred assets for investments exceeding specified amount							0.50%
Base management fee payable as a percentage of average closing price per share of common shares on NYSE							0.70%
Base management fee payable as a percentage of average market capitalization exceeding specified amount							0.50%
Incentive management fee payable (as a percent)	12
Period of measurement	3 years
Shorter period applicable in the case of calculation of the incentive management fee for 2014	1 year
Period applicable in the case of calculation of the incentive management fee for 2015	2 years
Base management fee payable monthly in cash (as a percent)	90.00%
Management fee payable in common shares (as a percent)	10.00%
Portion of shares issued in payment of an incentive management fee	0.3333%
Portion of remaining shares to be vested in equal annual installments	0.6666%
Number of equal annual installments for vesting of common shares | installment	2
RMR LLC | Amended Agreement | Maximum
Related Party Transaction [Line Items]
Threshold amount of other real estate investments for payment of base management fee							$ 250,000
Base management fee payable, average market capitalization							$ 250,000
RMR LLC | Up C Transaction | Amended Agreement
Related Party Transaction [Line Items]
Period of prior written notice for termination of the service agreements by the related party				120 days
Number of business days notice for termination of either agreement by related party before amendment, if entity undergoes a change of control				60 days
Number of business days notice for termination of either agreement by related party, if entity undergoes a change of control				5 days
Number of business days notice for termination of property management agreement for convenience by the related party		60 days
Number of business days notice for termination of property management agreement for performance by the related party		60 days
Window for providing notice of termination of property management agreement for performance by the related party		60 days
Window for providing notice of termination of property management agreement after change of control by the related party		12 months
Number of terminated management agreements for convenience before termination fee is incurred | agreement		1
Number of RMR LLC terminated management agreements for good cause before termination fee is incurred | agreement		1
Number of terminated management agreements for a performance reason before termination fee is incurred | agreement		1
Termination fee remaining term assumption		10 years
RMR LLC | Up C Transaction | Amended Agreement | Minimum
Related Party Transaction [Line Items]
Termination Fee Term		19 years
RMR LLC | Up C Transaction | Amended Agreement | Maximum
Related Party Transaction [Line Items]
Termination Fee Term		20 years