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Related Person Transactions - Investment in RMR Inc (Details) $ in Thousands | 1 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Mar. 31, 2017 building | Jun. 30, 2018 USD ($) building agreement shares | Dec. 31, 2017 USD ($)
Related person transactions |  |  |
Number of buildings included in joint venture agreement | building | 2 |  |
RMR Inc | Class A common shares |  |  |
Related person transactions |  |  |
Number of management agreements | agreement |  | 2 |
Equity securities investment (in shares) | shares |  | 2,637,408 |
AIC |  |  |
Related person transactions |  |  |
Property insurance annual premium | $ |  | $ 4,613 |
Equity method investments | $ |  | $ 8,153 | $ 8,185
MOBs |  |  |
Related person transactions |  |  |
Standalone insurance policy coverage period |  | 1 year |
Number of buildings included in joint venture agreement | building |  | 2 |

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