Fair Value of Assets and Liabilities - Recurring and Nonrecurring Assets (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016
Fair Value of Assets and Liabilities
Common shares owned in RMR Inc. (in shares)	1,214,225
Historical cost	$ 26,888
Unrealized gain on investment in available for sale securities	12,142	$ 12,871
Recurring
Fair Value of Assets and Liabilities
Investment in RMR Inc.	60,104
Recurring \| Level 1 inputs
Fair Value of Assets and Liabilities
Investment in RMR Inc.	60,104
Nonrecurring \| Discontinued Operations, Held-for-sale
Fair Value of Assets and Liabilities
Property held for sale and classified as discontinued operations	12,260
Nonrecurring \| Level 3 inputs \| Discontinued Operations, Held-for-sale
Fair Value of Assets and Liabilities
Property held for sale and classified as discontinued operations	12,260
Other Comprehensive Income (Loss)
Fair Value of Assets and Liabilities
Unrealized gain on investment in available for sale securities	$ 33,216

Common shares owned accounted for as available for sale securities.

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- Definition

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

+ References

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- Definition

Represents the historical cost during the period

+ References

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27357-111563

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- Definition

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19190-110258

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