Segment Information - Financial Information for Business Segments - Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Sep. 30, 2020
Segment Reporting Information [Line Items]
Total assets	$ 1,614,732	$ 1,559,125
Reportable Segments
Segment Reporting Information [Line Items]
Total assets	1,297,984	1,248,452
Reportable Segments | Brooks Semiconductor Solutions Group
Segment Reporting Information [Line Items]
Total assets	307,454	296,289
Reportable Segments | Brooks Life Sciences Products
Segment Reporting Information [Line Items]
Total assets	225,302	214,196
Reportable Segments | Brooks Life Sciences Services
Segment Reporting Information [Line Items]
Total assets	$ 765,228	$ 737,967