Shareholders’ Equity - Additional Information (Details) $ / shares in Units, $ in Thousands			3 Months Ended				6 Months Ended
	Apr. 27, 2020 USD ($) $ / shares shares	Mar. 11, 2020 $ / shares shares	Mar. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares	Mar. 31, 2019 USD ($) $ / shares	Dec. 31, 2018 USD ($) $ / shares	Mar. 31, 2020 USD ($) vesting_installment $ / shares shares	Mar. 31, 2019 USD ($) $ / shares	Sep. 30, 2019 shares
Class of Stock [Line Items]
Number of Vesting Installments | vesting_installment							5
General and administrative			$ 7,297		$ 7,122		$ 14,343	$ 14,442
Equity based compensation expense			$ 592		$ 448		$ 1,226	$ 943
Unvested shares outstanding (in shares) | shares			116,510				116,510
RMR LLC | RMR LLC
Class of Stock [Line Items]
Dividends paid (in dollars per share) | $ / shares			$ 0.30	$ 0.30	$ 0.30	$ 0.30	$ 0.60	$ 0.60
Value of dividends			$ 9,390	$ 9,391	$ 9,369	$ 9,369	$ 18,781	$ 18,738
Subsequent Event | RMR LLC | RMR LLC
Class of Stock [Line Items]
Value of dividends	$ 9,394
Class A Common Stock
Class of Stock [Line Items]
Shares granted during period (in shares) | shares		3,000
Share price (in dollars per share) | $ / shares		$ 31.28
General and administrative			$ 469
Shares repurchased (in shares) | shares							2,421
Shares repurchased during period							$ 95
Common stock shares outstanding (in shares) | shares			15,314,479				15,314,479		15,302,710
Class A Common Stock | ABP Trust
Class of Stock [Line Items]
Value of dividends			$ 4,500	$ 4,500	$ 4,500	$ 4,500	$ 9,000	$ 9,000
Common stock shares outstanding (in shares) | shares			15,000,000				15,000,000
Class A Common Stock | ABP Trust | Subsequent Event
Class of Stock [Line Items]
Value of dividends	$ 4,500
Class A and B-1 common shares
Class of Stock [Line Items]
Dividends paid (in dollars per share) | $ / shares			$ 0.38	$ 0.38	$ 0.35	$ 0.35	$ 0.76	$ 0.70
Value of dividends			$ 6,194	$ 6,195	$ 5,680	$ 5,680	$ 12,389	$ 11,360
Class A and B-1 common shares | RMR LLC
Class of Stock [Line Items]
Value of dividends			$ 4,890	$ 4,891	$ 4,869	$ 4,869	$ 9,781	$ 9,738
Class A and B-1 common shares | Subsequent Event
Class of Stock [Line Items]
Dividends paid (in dollars per share) | $ / shares	$ 0.38
Value of dividends	$ 6,200
Common stock shares outstanding (in shares) | shares	16,314,479
Class A and B-1 common shares | Subsequent Event | RMR LLC
Class of Stock [Line Items]
Dividends paid (in dollars per share) | $ / shares	$ 0.30
Value of dividends	$ 4,894
Vesting 2020
Class of Stock [Line Items]
Shares vesting (in shares) | shares							42,310
Vesting 2021
Class of Stock [Line Items]
Shares vesting (in shares) | shares							34,040
Vesting 2022
Class of Stock [Line Items]
Shares vesting (in shares) | shares							25,080
Vesting 2023
Class of Stock [Line Items]
Shares vesting (in shares) | shares							15,080