Related Person Transactions - Narrative (Details)	Mar. 31, 2021 shares
Five Star
Related Party Transaction [Line Items]
Ownership percentage	6.30%
SVC
Related Party Transaction [Line Items]
Ownership percentage	1.10%
ILPT
Related Party Transaction [Line Items]
Ownership percentage	1.20%
OPI
Related Party Transaction [Line Items]
Ownership percentage	1.50%
DHC
Related Party Transaction [Line Items]
Ownership percentage	1.10%
TA
Related Party Transaction [Line Items]
Ownership percentage	4.50%
RMRM
Related Party Transaction [Line Items]
Ownership percentage	2.30%
TRMT
Related Party Transaction [Line Items]
Ownership percentage	19.40%
ABP Trust | Class A Common Stock
Related Party Transaction [Line Items]
Common stock shares outstanding (in shares)	160,502
ABP Trust | Class A Units
Related Party Transaction [Line Items]
Common stock shares outstanding (in shares)	15,000,000
RMR LLC | TA
Related Party Transaction [Line Items]
Ownership percentage	4.30%