Condensed Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended						9 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2020	Jun. 30, 2019
Revenues:
Revenue	$ 138,649			$ 143,715			$ 439,402	$ 554,124
Expenses:
Compensation and benefits	29,569			28,530			89,888	85,523
Equity based compensation	1,299			1,334			3,183	4,349
Separation costs	0			239			645	7,050
Total compensation and benefits expense	30,868			30,103			93,716	96,922
General and administrative	6,335			7,670			20,678	22,112
Other client company reimbursable expenses	85,650			85,689			267,852	257,088
Transaction and acquisition related costs	427			42			1,596	273
Depreciation and amortization	229			250			731	762
Total expenses	123,509			123,754			384,573	377,157
Operating income (loss)	15,140			19,961			54,829	176,967
Interest and other income	727			2,408			4,102	6,402
Impairment loss on Tremont Mortgage Trust investment	0			(6,213)			0	(6,213)
Equity in earnings of investees	458			174			1,037	318
Unrealized gain (loss) on equity method investment accounted for under the fair value option	1,678			(731)			916	(2,978)
Income (loss) before income tax expense	18,003			15,599			60,884	174,496
Income tax expense	(2,608)			(2,226)			(8,944)	(24,335)
Net income (loss)	15,395	$ 14,921	$ 21,624	13,373	$ 18,708	$ 118,080	51,940	150,161
Net income attributable to noncontrolling interest	(8,678)			(7,524)			(29,306)	(83,935)
Net income attributable to The RMR Group Inc.	$ 6,717			$ 5,849			$ 22,634	$ 66,226
Weighted average common shares outstanding - basic (in shares)	16,198			16,137			16,187	16,126
Weighted average common shares outstanding - diluted (in shares)	31,198			16,149			31,187	16,142
Net income attributable to RMR Inc. per common share - basic (in dollars per share)	$ 0.41			$ 0.36			$ 1.39	$ 4.08
Net income attributable to RMR Inc. per common share - diluted (in dollars per share)	$ 0.41			$ 0.36			$ 1.37	$ 4.08
Total management and advisory services revenues
Revenues:
Revenue	$ 39,250			$ 44,443			$ 131,473	$ 256,168
Management services
Revenues:
Revenue	38,625			43,641			129,221	133,729
Incentive business management fees
Revenues:
Revenue	0			0			0	120,094
Advisory services
Revenues:
Revenue	625			802			2,252	2,345
Total reimbursable costs
Revenues:
Revenue	99,399			99,272			307,929	297,956
Reimbursable compensation and benefits
Revenues:
Revenue	13,749			13,583			40,077	40,868
Other client company reimbursable expenses
Revenues:
Revenue	$ 85,650			$ 85,689			$ 267,852	$ 257,088