Earnings per Share - Tabular Disclosure (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Net income
Income from continuing operations	$ 2,858	$ 2,706
Income from discontinued operations, net of tax	40,462	23,322
Net income	43,320	26,028
Net income attributable to Brooks Automation, Inc. - basic	43,320	26,028
Net income attributable to Brooks Automation, Inc. - diluted	$ 43,320	$ 26,028
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)	74,630	74,021
Dilutive restricted stock units	236	262
Weighted average common shares outstanding used in computing diluted earnings per share (in shares)	74,866	74,283
Basic net income per share:
Income from continuing operations (in dollars per share)	$ 0.04	$ 0.04
Income from discontinued operations, net of tax (in dollars per share)	0.54	0.32
Basic net income per share (in dollars per share)	0.58	0.35
Diluted net income per share:
Income from continuing operations (in dollars per share)	0.04	0.04
Income from discontinued operations, net of tax (in dollars per share)	0.54	0.31
Diluted net income per share (in dollars per share)	0.58	0.35
Dividend declared per share (in dollars per share)	$ 0.10	$ 0.10