Earnings per Share - Tabular Disclosure (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Income (loss) from continuing operations	$ (2,829)	$ 62,497	$ 3,437	$ 64,116
Income from discontinued operations, net of tax	6,250	4,523	14,399	19,390
Net income	$ 3,421	$ 67,020	$ 17,836	$ 83,506
Weighted average common shares outstanding used in computing basic earnings per share (in shares)	72,077	70,220	71,760	70,340
Dilutive restricted stock units	215	393	455	568
Weighted average common shares outstanding used in computing diluted earnings per share (in shares)	72,292	70,613	72,215	70,908
Basic net income per share attributable to Brooks Automation, Inc. common stockholders:
Income (loss) from continuing operations	$ (0.04)	$ 0.89	$ 0.05	$ 0.91
Income from discontinued operations, net of tax (in dollars per share)	0.09	0.06	0.20	0.28
Basic net income per share attributable to Brooks Automation, Inc. (in dollars per share)	0.05	0.95	0.25	1.19
Diluted net income per share attributable to Brooks Automation, Inc. common stockholders:
Income (loss) from continuing operations	(0.04)	0.89	0.05	0.90
Income from discontinued operations, net of tax (in dollars per share)	0.09	0.06	0.20	0.27
Diluted net income per share attributable to Brooks Automation, Inc. common stockholders (in dollars per share)	0.05	0.95	0.25	1.18
Dividend declared per share (in dollars per share)	$ 0.10	$ 0.10	$ 0.20	$ 0.20