Segment Information - Reconciliation of Reportable Segment Operating Income (Loss) to Corresponding Consolidated Amounts (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Total revenue	$ 210,500	$ 179,368
Amortization of intangible assets	10,600	7,800
Acquisition accounting impact on inventory contracts acquired		184
Operating income	10,666	5,333
Restructuring charges	576	59
Interest income	699	423
Interest expense	(737)	(5,290)
Other expenses, net	(417)	(30)
Income before income taxes	10,211	436
Brooks Semiconductor Solutions Group
Segment Reporting Information [Line Items]
Total revenue	118,811	112,707
Operating income	15,000	17,263
Brooks Life Sciences
Segment Reporting Information [Line Items]
Total revenue	91,689	66,661
Operating income	5,974	2,660
Segment Reconciling Items
Segment Reporting Information [Line Items]
Operating income	20,974	19,923
Corporate, Non-Segment
Segment Reporting Information [Line Items]
Other unallocated corporate (income) expenses	(852)	6,571
Completed Technology
Segment Reporting Information [Line Items]
Amortization of intangible assets	2,674	2,007
Acquired Intangible Assets
Segment Reporting Information [Line Items]
Amortization of intangible assets	$ 7,910	$ 5,769