Leases - Assets and Liabilities - Finance Leases (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Sep. 30, 2020
Finance Lease, Right-of-Use Asset, after Accumulated Amortization [Abstract]
Property, plant and equipment, at cost	$ 2,252	$ 2,540
Accumulated amortization	(1,557)	(1,246)
Property, plant and equipment, net	$ 695	1,294
Finance Lease, Right-of-Use Asset, Statement of Financial Position	us-gaap:PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization
Finance Lease Liability [Abstract]
Accrued expenses and other current liabilities	$ 1,022	1,135
Finance Lease Liability Current, Statement of Financial Position	brks:AccruedExpensesAndOtherCurrentLiabilities
Other long-term liabilities	$ 158	348
Finance Lease Liability Non Current, Statement of Financial Position	us-gaap:OtherLiabilitiesNoncurrent
Total finance lease liabilities	$ 1,180	$ 1,483