Segment Information - Financial Information for Business Segments - Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Sep. 30, 2018
Segment Reporting Information [Line Items]
Total assets	$ 1,496,731	$ 1,095,257
Operating Segments
Segment Reporting Information [Line Items]
Total assets	1,204,835	675,033
Operating Segments | Brooks Semiconductor Solutions Group
Segment Reporting Information [Line Items]
Total assets	288,891	264,452
Operating Segments | Brooks Life Sciences
Segment Reporting Information [Line Items]
Total assets	$ 915,944	$ 410,581