Related Party Transactions - Up-C Transaction (Details) $ / shares in Units, $ in Thousands								3 Months Ended	6 Months Ended	12 Months Ended
	Dec. 15, 2015 $ / shares	Dec. 14, 2015 shares	Nov. 23, 2015 $ / shares	Aug. 24, 2015 $ / shares	Jun. 05, 2015 USD ($) trust shares	May. 25, 2015 $ / shares	Feb. 26, 2015 $ / shares	Dec. 31, 2015 USD ($) shares	Dec. 31, 2015 shares	Dec. 31, 2015 USD ($) Vote employee shares	Dec. 31, 2014 shares
Related Party Transaction
Common shares owned in RMR Inc.								1,214,225	1,214,225	1,214,225
Common shares held								71,126,308	71,126,308	71,126,308	70,349,227
Noncash Acquisition Value Gain Loss | $								$ 12,368
Cash dividend paid (in dollars per share) | $ / shares			$ 0.43	$ 0.43		$ 0.43	$ 0.43
RMR Inc | Class A common shares
Related Party Transaction
Cash dividend paid (in dollars per share) | $ / shares	$ 0.5260
Cash dividend received | $										$ 811
RMR Inc | Class B1 common shares
Related Party Transaction
Cash dividend paid (in dollars per share) | $ / shares	$ 0.5260
Up C Transaction | Class A common shares
Related Party Transaction
Common shares owned in RMR Inc.								1,214,225	1,214,225	1,214,225
Up C Transaction | SIR | Class A common shares
Related Party Transaction
Common shares held								441,056	441,056	441,056
Up C Transaction | RMR LLC
Related Party Transaction
Additional consideration needed to cancel RMR Inc B-2 common stock | $										$ 0
Up C Transaction | RMR Inc | Class A common shares
Related Party Transaction
Shares issued in connection with acquisition					1,541,201
Noncash Acquisition Value Gain Loss | $								$ 12,368
Up C Transaction | RMR Inc | Class A member units
Related Party Transaction
Shares issued in connection with acquisition		768,032
Up C Transaction | ABP Trust formerly known as RMR trust
Related Party Transaction
Direct and indirect economic interest in RMR LLC as a percent					51.60%
Voting power of outstanding capital stock of RMR Inc					91.40%
RMR Inc | Up C Transaction
Related Party Transaction
Number of other companies to whom management services were provided by related party | trust					3
Aggregate consideration paid | $					$ 3,917
Equity conversion ratio of RMR Inc class B-1 common stock										1
Equity conversion ratio of RMR LLC class A membership units										1
RMR Inc | Up C Transaction | Common Shares
Related Party Transaction
Shares issued in connection with acquisition					700,000
RMR Inc | Up C Transaction | Class A common shares
Related Party Transaction
Number of votes per equity interest | Vote										1
RMR Inc | Up C Transaction | Class B1 common shares
Related Party Transaction
Number of votes per equity interest | Vote										10
RMR Inc | Up C Transaction | Class B2 common shares
Related Party Transaction
Number of votes per equity interest | Vote										10
Economic interest in RMR Inc as a percent										0.00%
RMR Inc | Up C Transaction | HPT
Related Party Transaction
Aggregate consideration paid | $					$ 12,622
RMR Inc | Up C Transaction | HPT | Common Shares
Related Party Transaction
Shares issued in connection with acquisition					1,490,000
RMR Inc | Up C Transaction | HPT | Class A common shares
Related Party Transaction
Common shares held								2,503,777	2,503,777	2,503,777
RMR Inc | Up C Transaction | SIR
Related Party Transaction
Aggregate consideration paid | $					$ 15,880
RMR Inc | Up C Transaction | SIR | Common Shares
Related Party Transaction
Shares issued in connection with acquisition					880,000
RMR Inc | Up C Transaction | SIR | Class A common shares
Related Party Transaction
Common shares held								1,586,836	1,586,836	1,586,836
RMR Inc | Up C Transaction | SNH
Related Party Transaction
Aggregate consideration paid | $					$ 13,967
RMR Inc | Up C Transaction | SNH | Common Shares
Related Party Transaction
Shares issued in connection with acquisition					2,345,000
RMR Inc | Up C Transaction | SNH | Class A common shares
Related Party Transaction
Common shares held								2,637,408	2,637,408	2,637,408
RMR Inc | Up C Transaction | RMR LLC
Related Party Transaction
Aggregate consideration paid | $					$ 11,520
RMR Inc | Up C Transaction | RMR LLC | Class B member units
Related Party Transaction
Shares issued in connection with acquisition					1,000,000
RMR LLC
Related Party Transaction
Number of employees | employee										0
Number of agreements with RMR LLC to provide management services | employee										2
RMR LLC | Class A common shares
Related Party Transaction
Shares issued in connection with acquisition		768,032
RMR LLC | Up C Transaction | RMR Inc | Class A member units
Related Party Transaction
Business acquisition related party equity interests delivered					30,000,000
HPT | Up C Transaction | RMR Inc | Class A common shares
Related Party Transaction
Shares issued in connection with acquisition					5,019,121
SIR | Up C Transaction | RMR Inc | Class A common shares
Related Party Transaction
Shares issued in connection with acquisition					3,166,891
SNH | Up C Transaction | RMR Inc | Class A common shares
Related Party Transaction
Shares issued in connection with acquisition					5,272,787
ABP Trust formerly known as RMR trust | Up C Transaction | RMR LLC | Class A member units
Related Party Transaction
Business acquisition related party equity interests delivered					15,000,000
ABP Trust formerly known as RMR trust | Up C Transaction | RMR Inc | Class B1 common shares
Related Party Transaction
Shares issued in connection with acquisition					1,000,000
ABP Trust formerly known as RMR trust | Up C Transaction | RMR Inc | Class B2 common shares
Related Party Transaction
Shares issued in connection with acquisition					15,000,000
Managing Trustees Barry And Adam Portnoy Member | Up C Transaction | ABP Trust formerly known as RMR trust
Related Party Transaction
Number of shares under lock up and registration agreement									700,000
Period over which shares remain under lock up and registration agreement									10 years