Goodwill and Intangible Assets - Goodwill Roll Forward (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Goodwill [Roll Forward]
Goodwill, net of accumulated impairments, beginning balance	$ 255,876	$ 207,154
Acquisitions and adjustments	232,726	48,722
Goodwill, net of accumulated impairments, ending balance	488,602	255,876
Brooks Semiconductor Solutions Group
Goodwill [Roll Forward]
Goodwill, net of accumulated impairments, beginning balance	47,963	40,334
Acquisitions and adjustments	(116)	7,629
Goodwill, net of accumulated impairments, ending balance	47,847	47,963
Brooks Life Sciences
Goodwill [Roll Forward]
Goodwill, net of accumulated impairments, beginning balance	207,913	166,820
Acquisitions and adjustments	232,842	41,093
Goodwill, net of accumulated impairments, ending balance	$ 440,755	$ 207,913