CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) $ in Thousands	Total Brooks Automation, Inc. Stockholders' Equity Cumulative Effect, Period of Adoption, Adjustment	Total Brooks Automation, Inc. Stockholders' Equity	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit Cumulative Effect, Period of Adoption, Adjustment	Accumulated Deficit	Treasury Stock	Noncontrolling Interests in Subsidiaries	Cumulative Effect, Period of Adoption, Adjustment	Total
Beginning Balance at Sep. 30, 2017		$ 607,644	$ 833	$ 1,874,918	$ 15,213		$ (1,082,364)	$ (200,956)			$ 607,644
Beginning Balance (in shares) at Sep. 30, 2017			83,294,848
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under restricted stock and purchase plans, net		2,826	$ 8	2,818							2,826
Shares issued under restricted stock and purchase plans, net (in shares)			869,282
Stock-based compensation		19,822		19,822							19,822
Common stock dividends declared		(28,285)					(28,285)				(28,285)
Changes in unrealized losses on marketable securities		(111)			(111)						(111)
Actuarial losses, net of tax effects		136			136						136
Acquisition of noncontrolling interest		876		876					$ 111		987
Net income		116,575					116,575		$ (111)		116,464
Foreign currency translation adjustments		(1,651)			(1,651)						(1,651)
Ending Balance at Sep. 30, 2018	$ (859)	717,832	$ 841	1,898,434	13,587	$ (859)	(994,074)	(200,956)		$ (859)	717,832
Ending Balance (in shares) at Sep. 30, 2018			84,164,130
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under restricted stock and purchase plans, net		3,423	$ 16	3,407							3,423
Shares issued under restricted stock and purchase plans, net (in shares)			1,595,570
Stock-based compensation		20,113		20,113							20,113
Common stock dividends declared		(28,895)					(28,895)				(28,895)
Changes in unrealized losses on marketable securities		104			104						104
Actuarial losses, net of tax effects		(847)			(847)						(847)
Net income		437,416					437,416				437,416
Foreign currency translation adjustments		(9,333)			(9,333)						(9,333)
Ending Balance at Sep. 30, 2019		1,138,954	$ 857	1,921,954	3,511		(586,412)	(200,956)			$ 1,138,954
Ending Balance (in shares) at Sep. 30, 2019			85,759,700								72,297,831
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under restricted stock and purchase plans, net		4,595	$ 16	4,579							$ 4,595
Shares issued under restricted stock and purchase plans, net (in shares)			1,534,010
Stock-based compensation		16,317		16,317							16,317
Common stock dividends declared		(29,513)					(29,513)				(29,513)
Changes in unrealized losses on marketable securities		7			7						7
Actuarial losses, net of tax effects		(476)			(476)						(476)
Net income		64,853					64,853				64,853
Foreign currency translation adjustments		18,877			18,877						18,877
Ending Balance at Sep. 30, 2020		$ 1,213,614	$ 873	$ 1,942,850	$ 21,919		$ (551,072)	$ (200,956)			$ 1,213,614
Ending Balance (in shares) at Sep. 30, 2020			87,293,710								73,831,841