Restructuring Expenses - Summary of Restructuring Accruals and Certain Facility Closures (Detail) - USD ($)		3 Months Ended		6 Months Ended
	Oct. 01, 2019	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Restructuring Reserve [Roll Forward]
Accrual at September 30, 2019	$ 1,378,000			$ 1,378,000
Expense Additions		$ 0	$ 0	3,104,000	$ 0
Cash Payments				(2,956,000)
Restructuring Reserve, Accrual Adjustment				(1,378,000)
Accrual at March 31, 2020		148,000		148,000
Reclassification of accrued lease exit obligations to operating lease liabilities				1,378,000
Facilities charges
Restructuring Reserve [Roll Forward]
Accrual at September 30, 2019	1,378,000			1,378,000
Expense Additions				0
Cash Payments				0
Restructuring Reserve, Accrual Adjustment				(1,378,000)
Accrual at March 31, 2020		0		0
Reclassification of accrued lease exit obligations to operating lease liabilities				1,378,000
Employee separation
Restructuring Reserve [Roll Forward]
Accrual at September 30, 2019	0			0
Expense Additions				3,104,000
Cash Payments				(2,956,000)
Restructuring Reserve, Accrual Adjustment				0
Accrual at March 31, 2020		$ 148,000		148,000
Reclassification of accrued lease exit obligations to operating lease liabilities				$ 0
Accounting Standards Update 2016-02 | Facilities charges
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Accrual Adjustment	(1,400,000)
Reclassification of accrued lease exit obligations to operating lease liabilities	$ 1,400,000