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Related Person Transactions (Details) $ / shares in Units, $ in Thousands |  |  | 12 Months Ended |
--- | --- | --- | --- | ---
Feb. 13, 2020 USD ($) | Jul. 01, 2019 USD ($) $ / shares shares | Dec. 31, 2019 USD ($) party agreement | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) | Jan. 01, 2020 shares
Related Party Transaction [Line Items] |  |  |  |  |  |
Proceeds from sale of RMR Inc. common shares, net |  |  | $ 98,557 | $ 0 | $ 0 |
Equity method investments, carrying value |  |  | 1,571 | 142,027 |  |
Equity in earnings of an investee |  |  | 400 | 516 | 608 |
Equity in unrealized gain (loss) of an investee |  |  | $ 91 | (68) | 462 |
The RMR Group Inc |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |
Number of unrelated parties | party |  |  | 4 |  |  |
Office Portfolio |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |
Standalone insurance policy coverage period |  |  | 1 year |  |  |
Five Star |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |
Minimum percentage of ownership of lessee's voting stock above which the entity has the option to cancel all its rights |  |  | 9.80% |  |  |
RMR Inc. | Class A common shares |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |
Investment in common shares (in shares) | shares |  | 2,637,408 |  |  |  |
Sale of stock, price per share (in dollars per share) | $ / shares |  | $ 40.00 |  |  |  |
Proceeds from sale of RMR Inc. common shares, net |  | $ 98,557 |  |  |  |
Five Star |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |
Maximum percentage of any class of equity shares that can be acquired without approval |  |  | 9.80% |  |  |
Five Star | Subsequent Event |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |
Investment in common shares (in shares) | shares |  |  |  |  |  | 10,691,658
Percentage of total shares outstanding |  |  |  |  |  | 33.90%
RMR LLC |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |
Number of management agreements with related party | agreement |  |  | 2 |  |  |
Premium payable for combined directors' and officers', percentage |  |  | 3.00% |  |  |
Premium payable for combined directors' and officers' liability insurance policy |  |  | $ 167 | 253 | 255 |
RMR LLC | RMR Inc. | Year one |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |
Award vesting rights, percentage |  |  | 20.00% |  |  |
RMR LLC | RMR Inc. | Year two |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |
Award vesting rights, percentage |  |  | 20.00% |  |  |
RMR LLC | RMR Inc. | Year three |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |
Award vesting rights, percentage |  |  | 20.00% |  |  |
RMR LLC | RMR Inc. | Year four |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |
Award vesting rights, percentage |  |  | 20.00% |  |  |
RMR LLC | RMR Inc. | Year five |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |
Award vesting rights, percentage |  |  | 20.00% |  |  |
AIC |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |
Total premiums including taxes and fees |  |  | $ 4,413 | 2,433 | 3,607 |
Equity method investments, carrying value |  |  | 298 | 8,632 | 8,185 |
AIC | Subsequent Event |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |
Liquidation distribution | $ 9,000 |  |  |  |  |
RMR LLC |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |
Rental revenue from related party |  |  | $ 256 | $ 228 | $ 331 |
RMR LLC | Five Star | Subsequent Event |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |
Percentage of total shares outstanding |  |  |  |  |  | 6.30%

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