Related Person Transactions - Revenues from Related Parties (Details) - USD ($) $ in Thousands	3 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Related Party Transaction [Line Items]
Revenue from related parties	$ 217,913	$ 104,684
Revenue from unrelated parties	628	610
Total revenues	$ 218,541	$ 105,294
Percentage of revenues from related parties	99.70%	99.40%
Percentage of revenues from unrelated parties	0.30%	0.60%
Percentage of revenue from related parties, net	100.00%	99.98044%
Managed REITs
Related Party Transaction [Line Items]
Revenue from related parties	$ 208,110	$ 96,534
Percentage of revenues from related parties	95.20%	91.70%
GOV
Related Party Transaction [Line Items]
Revenue from related parties	$ 13,509	$ 8,225
Percentage of revenues from related parties	6.20%	7.80%
HPT
Related Party Transaction [Line Items]
Revenue from related parties	$ 86,066	$ 62,728
Percentage of revenues from related parties	39.40%	59.60%
SIR
Related Party Transaction [Line Items]
Revenue from related parties	$ 36,990	$ 10,957
Percentage of revenues from related parties	16.90%	10.40%
SNH
Related Party Transaction [Line Items]
Revenue from related parties	$ 71,545	$ 14,624
Percentage of revenues from related parties	32.70%	13.90%
Managed Operators
Related Party Transaction [Line Items]
Revenue from related parties	$ 7,029	$ 6,713
Percentage of revenues from related parties	3.20%	6.30%
Five Star
Related Party Transaction [Line Items]
Revenue from related parties	$ 2,690	$ 2,364
Percentage of revenues from related parties	1.20%	2.20%
Sonesta
Related Party Transaction [Line Items]
Revenue from related parties	$ 568	$ 543
Percentage of revenues from related parties	0.30%	0.50%
TA
Related Party Transaction [Line Items]
Revenue from related parties	$ 3,771	$ 3,806
Percentage of revenues from related parties	1.70%	3.60%
Other
Related Party Transaction [Line Items]
Revenue from related parties	$ 2,774	$ 1,437
Percentage of revenues from related parties	1.30%	1.40%
AIC
Related Party Transaction [Line Items]
Revenue from related parties	$ 60	$ 60
Percentage of revenues from related parties	0.00%	0.10%
RIF
Related Party Transaction [Line Items]
Revenue from related parties	$ 729	$ 606
Percentage of revenues from related parties	0.40%	0.60%
ABP Trust
Related Party Transaction [Line Items]
Revenue from related parties	$ 1,279	$ 771
Percentage of revenues from related parties	0.60%	0.70%
TRMT
Related Party Transaction [Line Items]
Revenue from related parties	$ 706	$ 0
Percentage of revenues from related parties	0.30%	0.00%

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No definition available.

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Amount of revenue, fees and commissions earned from transactions between (a) a parent company and its subsidiaries; (b) subsidiaries of a common parent; (c) an entity and trusts for the benefit of employees, for example, but not limited to, pension and profit-sharing trusts that are managed by or under the trusteeship of the entity's management; (d) an entity and its principal, owners, management, or members of their immediate families; and (e) affiliates.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1(e))
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07.1(c))
-URI http://asc.fasb.org/extlink&oid=6488393&loc=d3e606610-122999

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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