Restructuring Expenses - Additional Information (Detail)	12 Months Ended
	Sep. 30, 2017 USD ($) position	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($) position
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 4,471,000	$ 0	$ 17,500,000
Number of positions reduced | position	79		97
Facilities charges
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 1,729,000	0	$ 13,600,000
Employee separation
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 2,742,000	$ 0	$ 3,900,000