Fair Value of Assets and Liabilities - Recurring and Non-Recurring (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($) shares
Travel Centers of America LLC
Fair Value of Assets and Liabilities
Unrealized gain (loss) on securities included in cumulative other comprehensive income	$ 3,455
RMR Inc
Fair Value of Assets and Liabilities
Unrealized gain (loss) on securities included in cumulative other comprehensive income	$ 57,563
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
Recurring | Quoted prices in active markets for identical assets (Level 1) | Travel Centers of America LLC
Fair Value of Assets and Liabilities
Investment securities	20,862
Recurring | Quoted prices in active markets for identical assets (Level 1) | RMR Inc
Fair Value of Assets and Liabilities
Investment securities	123,937
Recurring | Significant other observable inputs (Level 2) | Travel Centers of America LLC
Fair Value of Assets and Liabilities
Investment securities	0
Recurring | Significant other observable inputs (Level 2) | RMR Inc
Fair Value of Assets and Liabilities
Investment securities	0
Recurring | Significant unobservable inputs (Level 3) | Travel Centers of America LLC
Fair Value of Assets and Liabilities
Investment securities	0
Recurring | Significant unobservable inputs (Level 3) | RMR Inc
Fair Value of Assets and Liabilities
Investment securities	0
Carrying amount | Recurring | Travel Centers of America LLC
Fair Value of Assets and Liabilities
Investment securities	20,862
Carrying amount | Recurring | RMR Inc
Fair Value of Assets and Liabilities
Investment securities	$ 123,937