Fair Value of Assets and Liabilities (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) shares
Travel Centers of America LLC
Fair Value of Assets and Liabilities
Shares included in investment securities (in shares) | shares	3,420,000
Quoted prices in active markets for identical assets (Level 1) | Travel Centers of America LLC
Fair Value of Assets and Liabilities
Shares included in investment securities (in shares) | shares	3,420,000
RMR Inc
Fair Value of Assets and Liabilities
Unrealized gain (loss) on securities included in cumulative other comprehensive income	$ 32,525
RMR Inc | Quoted prices in active markets for identical assets (Level 1)
Fair Value of Assets and Liabilities
Historical cost of securities	$ 66,374
Shares included in investment securities (in shares) | shares	2,503,777
RMR Inc | Recurring | Quoted prices in active markets for identical assets (Level 1) | RMR Inc
Fair Value of Assets and Liabilities
Investment securities	$ 98,899
RMR Inc | Recurring | Significant Other Observable Inputs (Level 2)
Fair Value of Assets and Liabilities
Investment securities	0
RMR Inc | Recurring | Significant Unobservable Inputs (Level 3)
Fair Value of Assets and Liabilities
Investment securities	0
RMR Inc | Carrying Amount | Recurring
Fair Value of Assets and Liabilities
Investment securities	98,899
Travel Centers of America LLC
Fair Value of Assets and Liabilities
Unrealized gain (loss) on securities included in cumulative other comprehensive income	6,875
Travel Centers of America LLC | Quoted prices in active markets for identical assets (Level 1)
Fair Value of Assets and Liabilities
Historical cost of securities	$ 17,407
Travel Centers of America LLC | Quoted prices in active markets for identical assets (Level 1) | Travel Centers of America LLC
Fair Value of Assets and Liabilities
Shares included in investment securities (in shares) | shares	3,420,000
Travel Centers of America LLC | Recurring | Quoted prices in active markets for identical assets (Level 1) | Travel Centers of America LLC
Fair Value of Assets and Liabilities
Investment securities	$ 24,282
Travel Centers of America LLC | Recurring | Significant Other Observable Inputs (Level 2)
Fair Value of Assets and Liabilities
Investment securities	0
Travel Centers of America LLC | Recurring | Significant Unobservable Inputs (Level 3)
Fair Value of Assets and Liabilities
Investment securities	0
Travel Centers of America LLC | Carrying Amount | Recurring
Fair Value of Assets and Liabilities
Investment securities	$ 24,282