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Shareholders' Equity - Compensation (Details) - $ / shares |  |  |  |  |  |  | 1 Months Ended |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Oct. 02, 2018 | Sep. 24, 2018 | Sep. 13, 2018 | May 22, 2018 | Mar. 29, 2018 | Jan. 01, 2018 | Sep. 30, 2018 | Sep. 30, 2017 | Dec. 29, 2017
Employees Of RMR LLC |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Share-based compensation, shares issued in period (in shares) |  |  | 105,800 |  |  |  | 105,800 | 88,100 |
Shares purchased to satisfy tax withholding and payment obligations, price per share (in dollars per share) |  | $ 17.56 | $ 19.11 |  |  |  |  |  |
Shares purchased to satisfy tax withholding and payment obligations (in shares) |  | 18,121 |  |  |  |  | 18,121 | 16,654 |
Former Employees Of RMR LLC |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Shares purchased to satisfy tax withholding and payment obligations, price per share (in dollars per share) |  |  |  |  |  |  |  |  | $ 19.15
Shares purchased to satisfy tax withholding and payment obligations (in shares) |  |  |  |  |  | 4,628 |  |  |
Trustees |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Share-based compensation, shares issued in period (in shares) |  |  |  | 3,000 | 3,000 |  |  |  |
Share-based compensation, equity instruments other than options, nonvested closing price (in dollars per share) |  |  |  |  | $ 15.66 |  |  |  |
Shares purchased to satisfy tax withholding and payment obligations, price per share (in dollars per share) |  |  |  | $ 16.56 |  |  |  |  |
Subsequent Event | Employees Of RMR LLC |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Shares purchased to satisfy tax withholding and payment obligations, price per share (in dollars per share) | $ 17.05 |  |  |  |  |  |  |  |
Shares purchased to satisfy tax withholding and payment obligations (in shares) | 250 |  |  |  |  |  |  |  |

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- Definition The weighted average of per share prices paid for shares purchased on the open market for issuance to employees under the plan. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5047-113901 + Details
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- Definition Number of share instruments newly issued under a share-based compensation plan. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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