Document and Entity Information - USD ($)	12 Months Ended
	Sep. 30, 2019	Dec. 06, 2019	Mar. 31, 2019
Document and Entity Information [Abstract]
Entity Central Index Key	0000933974
Document Type	10-K
Document Annual Report	true
Document Period End Date	Sep. 30, 2019
Document Transition Report	false
Entity File Number	0-25434
Entity Registrant Name	Brooks Automation, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	04-3040660
Entity Address, Address Line One	15 Elizabeth Drive
Entity Address, City or Town	Chelmsford
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	01824
City Area Code	978
Local Phone Number	262-2400
Title of 12(b) Security	Common Stock, $0.01 par value
Entity Listing, Par Value Per Share	$ 0.01
Trading Symbol	BRKS
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 1,545,043,570
Entity Common Stock, Shares Outstanding		73,617,759
Current Fiscal Year End Date	--09-30
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Amendment Flag	false