Restructuring - Summary of Restructuring Costs (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Restructuring Cost and Reserve [Line Items]
Restructuring costs	$ 8,706	$ 134	$ 677
Restructuring Charges Excluding CEO Transition Costs [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs	6,332
Restructuring Charges Excluding CEO Transition Costs [Member] | Severance, Other Termination Benefits and Related Costs [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs	5,012
Restructuring Charges Excluding CEO Transition Costs [Member] | Lease and Other Contract Termination Fees [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs	353
Restructuring Charges Excluding CEO Transition Costs [Member] | Loss on Fixed Asset Disposals and Inventory Scrap [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs	225
Restructuring Charges Excluding CEO Transition Costs [Member] | Other [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs	$ 742