Revenue from Contracts with Customers - Disaggregated By Timing (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Total revenue	$ 780,848	$ 631,560	$ 527,499
Brooks Semiconductor Solutions Group
Disaggregation of Revenue [Line Items]
Total revenue	446,669	435,018	378,790
Brooks Life Sciences
Disaggregation of Revenue [Line Items]
Total revenue	334,179	$ 196,542	$ 148,709
Point in time
Disaggregation of Revenue [Line Items]
Total revenue	540,116
Point in time | Brooks Semiconductor Solutions Group
Disaggregation of Revenue [Line Items]
Total revenue	442,876
Point in time | Brooks Life Sciences
Disaggregation of Revenue [Line Items]
Total revenue	97,240
Over time
Disaggregation of Revenue [Line Items]
Total revenue	240,732
Over time | Brooks Semiconductor Solutions Group
Disaggregation of Revenue [Line Items]
Total revenue	3,793
Over time | Brooks Life Sciences
Disaggregation of Revenue [Line Items]
Total revenue	$ 236,939