CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) $ in Thousands	Total Brooks Automation, Inc. Stockholders' Equity	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Treasury Stock	Noncontrolling Interests in Subsidiaries	Total
Beginning Balance at Sep. 30, 2016	$ 553,690	$ 821	$ 1,855,703	$ 15,166	$ (1,117,044)	$ (200,956)		$ 553,690
Beginning Balance (in shares) at Sep. 30, 2016		82,220,270
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under restricted stock and purchase plans, net	1,949	$ 12	1,937					1,949
Shares issued under restricted stock and purchase plans, net (in shares)		1,074,578
Stock-based compensation	17,278		17,278					17,278
Common stock dividend declared, at $0.40, $0.40 and $0.40 per share for fiscal years 2019, 2018 and 2017, respectively	(27,932)				(27,932)			(27,932)
Foreign currency translation adjustments	(221)			(221)				(221)
Changes in unrealized losses on marketable securities, net of tax effects of $1, $0, and $0 for fiscal years 2019, 2018 and 2017, respectively	2			2				2
Actuarial gains (loss), net of tax effects of $13, ($49) and ($74) for fiscal years 2019, 2018 and 2017	525			525				525
Net income	62,612				62,612			62,612
Pension settlement	(259)			(259)				(259)
Ending Balance at Sep. 30, 2017	607,644	$ 833	1,874,918	15,213	(1,082,364)	(200,956)		607,644
Ending 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 dividend declared, at $0.40, $0.40 and $0.40 per share for fiscal years 2019, 2018 and 2017, respectively	(28,285)				(28,285)			(28,285)
Foreign currency translation adjustments	(1,651)			(1,651)				(1,651)
Changes in unrealized losses on marketable securities, net of tax effects of $1, $0, and $0 for fiscal years 2019, 2018 and 2017, respectively	(111)			(111)				(111)
Actuarial gains (loss), net of tax effects of $13, ($49) and ($74) for fiscal years 2019, 2018 and 2017	136			136				136
Acquisition of noncontrolling interest	876		876				$ 111	987
Net income	116,575				116,575		$ (111)	116,464
Ending Balance at Sep. 30, 2018	717,832	$ 841	1,898,434	13,587	(994,074)	(200,956)		$ 717,832
Ending Balance (in shares) at Sep. 30, 2018		84,164,130						70,702,261
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 dividend declared, at $0.40, $0.40 and $0.40 per share for fiscal years 2019, 2018 and 2017, respectively	(28,895)				(28,895)			(28,895)
Foreign currency translation adjustments	(9,333)			(9,333)				(9,333)
Changes in unrealized losses on marketable securities, net of tax effects of $1, $0, and $0 for fiscal years 2019, 2018 and 2017, respectively	104			104				104
Actuarial gains (loss), net of tax effects of $13, ($49) and ($74) for fiscal years 2019, 2018 and 2017	(847)			(847)				(847)
Cumulative effect of adoption of ASC 606	(859)				(859)			(859)
Net income	437,416				437,416			437,416
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