Restructuring Expenses - Summary of Restructuring Accruals and Certain Facility Closures (Detail) - USD ($)	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Restructuring Reserve [Roll Forward]
Beginning balance	$ 8,305,000	$ 9,233,000
Expense additions	0	4,471,000	$ 0
Cash payments	(3,077,000)	(5,399,000)
Ending balance	5,228,000	8,305,000	9,233,000
Less: current portion	(3,850,000)	(3,077,000)	(4,266,000)
Non-current	1,378,000	5,228,000	4,967,000
Facilities charges
Restructuring Reserve [Roll Forward]
Beginning balance	8,120,000	9,233,000
Expense additions		1,729,000
Cash payments	(2,892,000)	(2,842,000)
Ending balance	5,228,000	8,120,000	9,233,000
Employee separation
Restructuring Reserve [Roll Forward]
Beginning balance	185,000	0
Expense additions		2,742,000
Cash payments	(185,000)	(2,557,000)
Ending balance	$ 0	$ 185,000	$ 0