Goodwill and Intangible Assets - Components of Goodwill by Business Segment (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Goodwill [Roll Forward]
Gross goodwill, period start	$ 736,366	$ 724,459
Acquisitions and adjustments during fiscal year	80,730	11,907
Gross goodwill, period end	817,096	736,366
Accumulated goodwill impairments, beginning balance	(614,958)	(614,958)
Accumulated goodwill impairments, ending balance	(614,958)	(614,958)
Goodwill, less accumulated impairments	202,138	121,408	$ 109,501
Brooks Semiconductor Solutions Group
Goodwill [Roll Forward]
Gross goodwill, period start	654,727	651,067
Acquisitions and adjustments during fiscal year	1,054	3,660
Gross goodwill, period end	655,781	654,727
Accumulated goodwill impairments, beginning balance	(588,944)	(588,944)
Accumulated goodwill impairments, ending balance	(588,944)	(588,944)
Goodwill, less accumulated impairments	66,837	65,783	62,123
Brooks Life Science Systems
Goodwill [Roll Forward]
Gross goodwill, period start	55,625	47,378
Acquisitions and adjustments during fiscal year	79,676	8,247
Gross goodwill, period end	135,301	55,625
Accumulated goodwill impairments, beginning balance	0	0
Accumulated goodwill impairments, ending balance	0	0
Goodwill, less accumulated impairments	135,301	55,625	47,378
Other
Goodwill [Roll Forward]
Gross goodwill, period start	26,014	26,014
Acquisitions and adjustments during fiscal year	0	0
Gross goodwill, period end	26,014	26,014
Accumulated goodwill impairments, beginning balance	(26,014)	(26,014)
Accumulated goodwill impairments, ending balance	(26,014)	(26,014)
Goodwill, less accumulated impairments	$ 0	$ 0	$ 0