Segment Information - Financial Information for Business Segments - Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Sep. 30, 2020
Segment Reporting Information [Line Items]
Total assets	$ 1,763,255	$ 1,559,125
Operating Segments
Segment Reporting Information [Line Items]
Total assets	1,472,498	1,248,452
Operating Segments | Brooks Semiconductor Solutions Group
Segment Reporting Information [Line Items]
Total assets	433,108	296,289
Operating Segments | Brooks Life Sciences Products
Segment Reporting Information [Line Items]
Total assets	259,592	214,196
Operating Segments | Brooks Life Sciences Services
Segment Reporting Information [Line Items]
Total assets	$ 779,798	$ 737,967