Reconciliation of Weighted Average Common Shares Outstanding for Purposes of Calculating Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2010
Earnings Per Share Disclosure [Line Items]
Net income attributable to Brooks Automation, Inc.	$ 136,789	$ 130,385	$ 59,841
Weighted average common shares outstanding used in computing basic earnings per share	65,128	64,549	63,777
Dilutive common stock options and restricted stock awards	594	454	397
Weighted average common shares outstanding for purposes of computing diluted earnings per share	65,722	65,003	64,174
Basic net income per share attributable to Brooks Automation, Inc. common stockholders	$ 2.10	$ 2.02	$ 0.94
Diluted net income per share attributable to Brooks Automation, Inc. common stockholders	$ 2.08	$ 2.01	$ 0.93