Restructuring Expenses - Summary of Restructuring Accruals and Certain Facility Closures (Detail) - USD ($)	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Restructuring Reserve [Roll Forward]
Beginning balance	$ 9,233,000	$ 15,400,000
Expense additions	4,471,000	0	$ 17,500,000
Cash payments	(5,399,000)	(6,167,000)
Ending balance	8,305,000	9,233,000	15,400,000
Less: current portion	(3,077,000)	(4,266,000)	(5,570,000)
Non-current	5,228,000	4,967,000	9,830,000
Facilities charges
Restructuring Reserve [Roll Forward]
Beginning balance	9,233,000	12,995,000
Expense additions	1,729,000	0	13,600,000
Cash payments	(2,842,000)	(3,762,000)
Ending balance	8,120,000	9,233,000	12,995,000
Employee separation
Restructuring Reserve [Roll Forward]
Beginning balance	0	2,405,000
Expense additions	2,742,000	0	3,900,000
Cash payments	(2,557,000)	(2,405,000)
Ending balance	$ 185,000	$ 0	$ 2,405,000