Document and Entity Information - $ / shares	3 Months Ended
	Dec. 31, 2018	Jan. 31, 2019
Document and Entity Information [Abstract]
Trading Symbol	BRKS
Entity Registrant Name	BROOKS AUTOMATION INC
Entity Central Index Key	0000933974
Current Fiscal Year End Date	--09-30
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Entity Small Business	false
Entity Emerging Growth Company	false
Amendment Flag	false
Entity Current Reporting Status	Yes
Entity Common Stock, Shares Outstanding		70,960,094
Entity Listing, Par Value Per Share	$ 0.01