Goodwill and Intangible Assets - Reporting Units (Details) - segment	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Goodwill [Line Items]
Number of reporting units	6	6	6
Brooks Semiconductor Solutions Group
Goodwill [Line Items]
Number of reporting units	3	3	3
Brooks Life Sciences Products
Goodwill [Line Items]
Number of reporting units	1	1	1
Brooks Life Sciences Services
Goodwill [Line Items]
Number of reporting units	2	2	2