Earnings per Share - Tabular Disclosure (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
(Loss) income from continuing operations	$ 9,554	$ 67,717	$ 10,687
Income from discontinued operations, net of tax	427,862	48,747	51,925
Net income	437,416	116,464	62,612
Net loss attributable to noncontrolling interest		111
Net income attributable to Brooks Automation, Inc.	$ 437,416	$ 116,575	$ 62,612
Weighted average common shares outstanding used in computing basic earnings per share (in shares)	71,992	70,489	69,575
Dilutive restricted stock units	394	448	910
Weighted average common shares outstanding used in computing diluted earnings per share (in shares)	72,386	70,937	70,485
Basic net income per share attributable to Brooks Automation, Inc. common stockholders:
Income from continuing operations	$ 0.13	$ 0.96	$ 0.15
Income from discontinued operations, net of tax	5.95	0.69	0.75
Basic net income per share attributable to Brooks Automation, Inc. (in dollars per share)	6.08	1.65	0.90
Diluted net income per share attributable to Brooks Automation, Inc. common stockholders:
Income from continuing operations	0.13	0.95	0.15
Income from discontinued operations, net of tax	5.91	0.69	0.74
Diluted net income per share attributable to Brooks Automation, Inc. common stockholders (in dollars per share)	6.04	1.64	0.89
Dividend declared per share (in dollars per share)	$ 0.40	$ 0.40	$ 0.40