Fair Value of Assets and Liabilities - Recurring and Non-Recurring (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2016 USD ($) shares
Travel Centers of America LLC
Fair Value of Assets and Liabilities
Unrealized gain (loss) on securities included in cumulative other comprehensive income	$ 7,080
RMR Inc
Fair Value of Assets and Liabilities
Unrealized gain (loss) on securities included in cumulative other comprehensive income	$ 28,619
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
Historical cost of securities	$ 17,407
Quoted prices in active markets for identical assets (Level 1) | RMR Inc
Fair Value of Assets and Liabilities
Shares included in investment securities (in shares) | shares	2,503,777
Historical cost of securities	$ 66,374
Carrying amount | Recurring | Travel Centers of America LLC
Fair Value of Assets and Liabilities
Investment securities	24,487
Carrying amount | Recurring | RMR Inc
Fair Value of Assets and Liabilities
Investment securities	94,993
Fair value | Recurring | Quoted prices in active markets for identical assets (Level 1) | Travel Centers of America LLC
Fair Value of Assets and Liabilities
Investment securities	24,487
Fair value | Recurring | Quoted prices in active markets for identical assets (Level 1) | RMR Inc
Fair Value of Assets and Liabilities
Investment securities	94,993
Fair value | Recurring | Significant other observable inputs (Level 2) | Travel Centers of America LLC
Fair Value of Assets and Liabilities
Investment securities	0
Fair value | Recurring | Significant other observable inputs (Level 2) | RMR Inc
Fair Value of Assets and Liabilities
Investment securities	0
Fair value | Recurring | Significant unobservable inputs (Level 3) | Travel Centers of America LLC
Fair Value of Assets and Liabilities
Investment securities	0
Fair value | Recurring | Significant unobservable inputs (Level 3) | RMR Inc
Fair Value of Assets and Liabilities
Investment securities	$ 0