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Shareholders' Equity - Compensation (Details) - $ / shares | May 22, 2018 | Mar. 29, 2018 | Jan. 01, 2018 | Dec. 29, 2017
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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 (in shares) |  |  | 4,628 |
Shares purchased to satisfy tax withholding and payment obligations, price per share (in dollars per share) |  |  |  | $ 19.15
Trustees |  |  |  |
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) | $ 16.56 |  |  |
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 |  |

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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://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=96867065&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://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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