Earnings per Share - Tabular Disclosure (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Earnings Per Share [Abstract]
Income from continuing operations	$ 9,192	$ (2,829)	$ 22,366	$ 3,437
(Loss) income from discontinued operations, net of tax	(65)	6,250	(182)	14,399
Net income	$ 9,127	$ 3,421	$ 22,184	$ 17,836
Weighted average common shares outstanding used in computing basic earnings per share (in shares)	73,708	72,077	73,331	71,760
Dilutive restricted stock units	81	215	421	455
Weighted average common shares outstanding used in computing diluted earnings per share (in shares)	73,789	72,292	73,752	72,215
Basic net income per share attributable to Brooks Automation, Inc. common stockholders:
Income (loss) from continuing operations	$ 0.12	$ (0.04)	$ 0.30	$ 0.05
(Loss) income from discontinued operations, net of tax	0.00	0.09	0.00	0.20
Basic net income per share attributable to Brooks Automation, Inc. (in dollars per share)	0.12	0.05	0.30	0.25
Diluted net income per share:
Income (loss) from continuing operations	0.12	(0.04)	0.30	0.05
(Loss) income from discontinued operations, net of tax	0.00	0.09	0.00	0.20
Diluted net income per share attributable to Brooks Automation, Inc. common stockholders (in dollars per share)	0.12	0.05	0.30	0.25
Dividend declared per share (in dollars per share)	$ 0.10	$ 0.10	$ 0.20	$ 0.20