Restructuring Expenses - Summary of Restructuring Accruals and Certain Facility Closures (Detail) - USD ($)	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Restructuring Reserve [Roll Forward]
Beginning balance	$ 15,400,000	$ 262,000
Expense additions	0	17,479,000	$ 4,100,000
Cash payments	(6,167,000)	(1,765,000)
Non-cash settlements	0	(576,000)
Ending balance	9,233,000	15,400,000	262,000
Less: current portion	(4,266,000)	(5,570,000)	(262,000)
Non-current	4,967,000	9,830,000	0
Facilities charges
Restructuring Reserve [Roll Forward]
Beginning balance	12,995,000	92,000
Expense additions	0	13,571,000	200,000
Cash payments	(3,762,000)	(92,000)
Non-cash settlements	0	(576,000)
Ending balance	9,233,000	12,995,000	92,000
Employee separation
Restructuring Reserve [Roll Forward]
Beginning balance	2,405,000	170,000
Expense additions	0	3,908,000	3,900,000
Cash payments	(2,405,000)	(1,673,000)
Non-cash settlements	0	0
Ending balance	$ 0	$ 2,405,000	$ 170,000