Earnings per Share - Tabular Disclosure (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Income (loss) from continuing operations	$ 921	$ 4,813	$ 4,359	$ 68,929
Income from discontinued operations, net of tax	6,333	17,793	20,731	37,183
Net income	7,254	22,606	25,090	106,112
Net loss attributable to noncontrolling interest		111		111
Net income attributable to Brooks Automation, Inc.	$ 7,254	$ 22,717	$ 25,090	$ 106,223
Weighted average common shares outstanding used in computing basic earnings per share (in shares)	72,188	70,596	71,903	70,425
Dilutive restricted stock units	282	382	410	508
Weighted average common shares outstanding used in computing diluted earnings per share (in shares)	72,470	70,978	72,313	70,933
Basic net income per share attributable to Brooks Automation, Inc. common stockholders:
Income from continuing operations	$ 0.01	$ 0.07	$ 0.06	$ 0.98
Income from discontinued operations, net of tax	0.09	0.25	0.29	0.53
Basic net income per share attributable to Brooks Automation, Inc. (in dollars per share)	0.10	0.32	0.35	1.51
Diluted net income per share attributable to Brooks Automation, Inc. common stockholders:
Income from continuing operations	0.01	0.07	0.06	0.97
Income from discontinued operations, net of tax	0.09	0.25	0.29	0.52
Diluted net income per share attributable to Brooks Automation, Inc. common stockholders (in dollars per share)	0.10	0.32	0.35	1.50
Dividend declared per share (in dollars per share)	$ 0.10	$ 0.10	$ 0.30	$ 0.30