Earnings per Share - Tabular Disclosure (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Net income	$ 22,606	$ 17,350	$ 106,112	$ 45,226
Net loss attributable to noncontrolling interest	111		111
Net income attributable to Brooks Automation, Inc.	$ 22,717	$ 17,350	$ 106,223	$ 45,226
Weighted average common shares outstanding used in computing basic earnings (losses) per share (in shares)	70,596	69,711	70,425	69,496
Dilutive restricted stock units	382	694	508	702
Weighted average common shares outstanding used in computing diluted earnings (losses) per share (in shares)	70,978	70,405	70,933	70,198
Basic net income per share (in dollars per share)	$ 0.32	$ 0.25	$ 1.51	$ 0.65
Diluted net income per share (in dollars per share)	$ 0.32	$ 0.25	$ 1.50	$ 0.64