Document and Entity Information - USD ($)	12 Months Ended
	Sep. 30, 2018	Nov. 15, 2018	Mar. 31, 2018
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-K
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Public Float			$ 1,303,513,402
Entity Common Stock, Shares Outstanding		71,776,483
Entity Listing, Par Value Per Share	$ 0.01