Goodwill and Intangible Assets - Goodwill Roll Forward (Details) $ in Thousands	6 Months Ended
	Mar. 31, 2019 USD ($)
Goodwill [Roll Forward]
Goodwill, net of accumulated impairments, beginning balance	$ 255,876
Acquisitions and adjustments	236,650
Goodwill, net of accumulated impairments, ending balance	492,526
Brooks Semiconductor Solutions Group
Goodwill [Roll Forward]
Goodwill, net of accumulated impairments, beginning balance	47,963
Acquisitions and adjustments	(184)
Goodwill, net of accumulated impairments, ending balance	47,779
Brooks Life Sciences
Goodwill [Roll Forward]
Goodwill, net of accumulated impairments, beginning balance	207,913
Acquisitions and adjustments	236,834
Goodwill, net of accumulated impairments, ending balance	$ 444,747