Segment Reporting (Details) $ in Thousands	3 Months Ended								4 Months Ended	8 Months Ended	12 Months Ended
	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2015 USD ($)	Jun. 05, 2015 USD ($)	Sep. 30, 2016 USD ($) segment	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)
Segment Reporting
Number of segments | segment											1
Revenues
Management services											$ 226,660	$ 162,326	$ 218,753
Reimbursable payroll and related costs											37,660	28,230	64,049
Advisory services											2,620	2,380	2,244
Total revenues	$ 56,266	$ 52,211	$ 48,333	$ 110,130	$ 48,111	$ 48,179	$ 49,810	$ 46,836			266,940	192,936	285,046
Expenses
Compensation and benefits											91,985	83,456	127,841
Members profit sharing											0	0	116,000
Separation costs											1,358	116	2,330
General and administrative											25,129	26,535	21,957
Depreciation and amortization											1,768	2,117	2,446
Total expenses											120,240	112,224	270,574
Operating income											146,700	80,712	14,472
Interest and other income											234	1,732	497
Unrealized gains (losses) attributable to changes in fair value of stock accounted for under the fair value option											0	(290)	(4,556)
Income before income tax expense and equity in earnings of investee											146,934	82,154	10,413
Income tax expense											(24,573)	(4,848)	(280)
Equity in earnings of investee											0	115	160
Net income	18,832	$ 17,402	$ 15,748	$ 70,379	16,317	$ 16,273	$ 25,183	$ 19,648	$ 18,841	$ 58,580	122,361	77,421	10,293
Total assets	337,531				303,892				303,892		337,531	303,892	287,223
RMR LLC
Revenues
Management services											226,602	161,903	217,014
Reimbursable payroll and related costs											37,660	28,230	64,049
Total revenues											264,262	190,133	281,063
Expenses
Compensation and benefits											90,872	81,886	125,780
Members profit sharing													116,000
Separation costs											1,358	116	2,330
General and administrative											23,678	25,892	21,125
Depreciation and amortization											1,703	2,117	2,446
Total expenses											117,611	110,011	267,681
Operating income											146,651	80,122	13,382
Interest and other income											223	1,668	428
Unrealized gains (losses) attributable to changes in fair value of stock accounted for under the fair value option												(317)	(4,603)
Income before income tax expense and equity in earnings of investee											146,874	81,473	9,207
Income tax expense											(1)	60	(1)
Equity in earnings of investee												115	160
Net income											146,873	81,648	9,366
Total assets	277,802				255,531				255,531		277,802	255,531	281,533
All other operations
Revenues
Management services											58	423	1,739
Advisory services											2,620	2,380	2,244
Total revenues											2,678	2,803	3,983
Expenses
Compensation and benefits											1,113	1,570	2,061
General and administrative											1,451	643	832
Depreciation and amortization											65
Total expenses											2,629	2,213	2,893
Operating income											49	590	1,090
Interest and other income											11	64	69
Unrealized gains (losses) attributable to changes in fair value of stock accounted for under the fair value option												27	47
Income before income tax expense and equity in earnings of investee											60	681	1,206
Income tax expense											(24,572)	(4,908)	(279)
Net income											(24,512)	(4,227)	927
Total assets	$ 59,729				$ 48,361				$ 48,361		59,729	48,361	5,690
Intersegment Eliminations
Revenues
Total revenues											$ 1,806	$ 752	$ 1,276