Earnings per Share - Tabular Disclosure (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Income (loss) income from continuing operations	$ 67,717	$ 10,687	$ (85,457)
Income from discontinued operations, net of tax	48,747	51,925	15,981
Net income	116,464	62,612	(69,476)
Net loss attributable to noncontrolling interest	111
Net income (loss) attributable to Brooks Automation, Inc	$ 116,575	$ 62,612	$ (69,476)
Weighted average common shares outstanding used in computing basic earnings (losses) per share (in shares)	70,489	69,575	68,507
Dilutive restricted stock units	448	910
Weighted average common shares outstanding used in computing diluted earnings (losses) per share (in shares)	70,937	70,485	68,507
Basic net (loss) income per share attributable to Brooks Automation, Inc. common stockholders:
Income (loss) from continuing operations (in dollars per share)	$ 0.96	$ 0.15	$ (1.25)
Income from discontinued operations, net of tax (in dollars per share)	0.69	0.75	0.23
Basic net income (loss) per share attributable to Brooks Automation, Inc. (in dollars per share)	1.65	0.90	(1.01)
Diluted net income (loss) per share attributable to Brooks Automation, Inc. common stockholders:
Income (loss) from continuing operations (in dollars per share)	0.95	0.15	(1.25)
Income from discontinued operations, net of tax (in dollars per share)	0.69	0.74	0.23
Diluted net income (loss) per share attributable to Brooks Automation, Inc. common stockholders (in dollars per share)	$ 1.64	$ 0.89	$ (1.01)