Earnings per Share - Tabular Disclosure (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Net income
Income from continuing operations	$ (22,397)	$ (1,842)	$ (7,336)	$ 2,706	$ (581)	$ (9,858)	$ (10,603)	$ (5,320)	$ (28,869)	$ (26,362)	$ (61,127)
Income from discontinued operations, net of tax									139,616	91,215	498,543
Net income	$ 21,805	$ 39,166	$ 23,748	$ 26,028	$ 28,973	$ 13,696	$ 9,127	$ 13,057	110,747	64,853	437,416
Net income attributable to Brooks Automation, Inc. - basic									110,747	64,853	437,416
Net income attributable to Brooks Automation, Inc. - diluted									$ 110,747	$ 64,853	$ 437,416
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)									74,229	73,557	71,992
Dilutive restricted stock units									226	293	394
Weighted average common shares outstanding used in computing diluted earnings per share (in shares)									74,455	73,850	72,386
Basic net income per share:
Loss from continuing operations (in dollars per share)									$ (0.39)	$ (0.36)	$ (0.85)
Income from discontinued operations, net of tax (in dollars per share)									1.88	1.24	6.92
Basic net income per share (in dollars per share)	$ 0.29	$ 0.53	$ 0.32	$ 0.35	$ 0.39	$ 0.19	$ 0.12	$ 0.18	1.49	0.88	6.08
Diluted net income per share:
Loss from continuing operations (in dollars per share)									(0.39)	(0.36)	(0.84)
Income from discontinued operations, net of tax (in dollars per share)									1.88	1.24	6.89
Diluted net income per share (in dollars per share)	$ 0.29	$ 0.53	$ 0.32	$ 0.35	$ 0.39	$ 0.19	$ 0.12	$ 0.18	1.49	0.88	6.04
Dividend declared per share (in dollars per share)									$ 0.40	$ 0.40	$ 0.40