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Amount classified as real estate properties attributable to disposal group held for sale or disposed of.

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Amount of unrealized gain (loss) on investments in debt and equity securities classified as available-for-sale securities.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-Section 50
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Fair value portion of investments in an entity not consolidated. Includes, but is not limited to, investments in an entity that is affiliated with the reporting entity by means of direct or indirect ownership, an entity in which the reporting entity shares control of the entity with another party or group, an entity which the company has significant influence, but does not have control and subsidiaries that are not required to be consolidated and are accounted for using the equity or cost method.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 1
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Fair Value of Assets and Liabilities - Asset Measured at Fair Value (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value of Assets and Liabilities
Common shares owned in RMR Inc.	1,214,225
Historical cost	$ 26,888
Unrealized gain on investment in available for sale securities	24,042	$ 30,465	$ (9,391)
Recurring
Fair Value of Assets and Liabilities
Investment in RMR Inc.	72,005
Recurring \| Level 1 inputs
Fair Value of Assets and Liabilities
Investment in RMR Inc.	72,005
Recurring \| Level 2 inputs
Fair Value of Assets and Liabilities
Investment in RMR Inc.	0
Recurring \| Level 3 inputs
Fair Value of Assets and Liabilities
Investment in RMR Inc.	0
Discontinued Operations, Held-for-sale \| Nonrecurring
Fair Value of Assets and Liabilities
Property held for sale and classified as discontinued operations	19,667
Discontinued Operations, Held-for-sale \| Nonrecurring \| Level 1 inputs
Fair Value of Assets and Liabilities
Property held for sale and classified as discontinued operations	0
Discontinued Operations, Held-for-sale \| Nonrecurring \| Level 2 inputs
Fair Value of Assets and Liabilities
Property held for sale and classified as discontinued operations	19,667
Discontinued Operations, Held-for-sale \| Nonrecurring \| Level 3 inputs
Fair Value of Assets and Liabilities
Property held for sale and classified as discontinued operations	0
Cumulative Other Comprehensive Income (Loss)
Fair Value of Assets and Liabilities
Unrealized gain on investment in available for sale securities	$ 45,117