Summary of Significant Accounting Policies - Equity Securities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jun. 05, 2015
Future liability amortization
Future amortization of liability, 2019	$ 3,585
Future amortization of liability, 2020	3,585
Future amortization of liability, 2021	3,585
Future amortization of liability, 2022	3,585
Future amortization of liability, 2023	3,585
Future amortization of liability, thereafter	$ 43,081
Travel Centers of America LLC
Debt and Equity Securities, FV-NI [Line Items]
Number of common shares owned (in shares)	3,420,000
Travel Centers of America LLC | Quoted Prices in Active Markets for Identical Assets (Level 1)
Debt and Equity Securities, FV-NI [Line Items]
Number of common shares owned (in shares)	3,420,000
RMR | Quoted Prices in Active Markets for Identical Assets (Level 1)
Debt and Equity Securities, FV-NI [Line Items]
Number of common shares owned (in shares)	2,503,777			2,503,777
RMR LLC | RMR Inc | Up C Transaction
Debt and Equity Securities, FV-NI [Line Items]
Investments original cost				$ 55,922
Fair value of investment				$ 129,722
Unamortized business management liabilities	$ 61,006
RMR LLC | RMR Inc | Up C Transaction | General and Administrative Expense
Debt and Equity Securities, FV-NI [Line Items]
Amortization of business management fees	$ 3,585	$ 3,585	$ 3,585