Stock-Based Compensation - Performance-Based Grants (Details)	3 Months Ended	12 Months Ended
Dec. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Performance-based awards granted, percentage (as a percent)		100.00%	100.00%	100.00%
Performance-based awards granted, percentage, maximum threshold met (as a percent)	200.00%
Performance goal measurement period (in years)	3 years

Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Percentage of Performance-based Units Awarded, Financial Metric, Maximum Threshold Met.

No definition available.

Name:	brks_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsPercentageOfPerformanceBasedUnitsAwardedFinancialMetricMaximumThresholdMet
Namespace Prefix:	brks_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration