Earnings per Share - Tabular Disclosure (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Net income
Income from continuing operations	$ 23,932	$ 9,192	$ 50,940	$ 22,366
Loss from discontinued operations, net of tax	(184)	(65)	(1,164)	(182)
Net income	23,748	9,127	49,776	22,184
Net income attributable to Brooks Automation, Inc. - basic	23,748	9,127	49,776	22,184
Net income attributable to Brooks Automation, Inc. - diluted	$ 23,748	$ 9,127	$ 49,776	$ 22,184
Weighted average common shares outstanding used in computing diluted earnings per share
Weighted average common shares outstanding used in computing basic earnings per share (in shares)	74,265	73,708	74,142	73,331
Dilutive restricted stock units	149	81	225	421
Weighted average common shares outstanding used in computing diluted earnings per share (in shares)	74,414	73,789	74,367	73,752
Basic net income per share:
Income from continuing operations (in dollars per share)	$ 0.32	$ 0.12	$ 0.69	$ 0.30
Loss from discontinued operations, net of tax (in dollars per share)	0.00	0.00	(0.02)	0.00
Basic net income per share attributable to Brooks Automation, Inc. (in dollars per share)	0.32	0.12	0.67	0.30
Diluted net income per share:
Income from continuing operations (in dollars per share)	0.32	0.12	0.68	0.30
Loss from discontinued operations, net of tax (in dollars per share)	0.00	0.00	(0.02)	0.00
Diluted net income per share (in dollars per share)	0.32	0.12	0.67	0.30
Dividend declared per share (in dollars per share)	$ 0.10	$ 0.10	$ 0.20	$ 0.20