Restructuring and Headquarters Relocation Charges - Additional Information (Details) $ in Thousands	3 Months Ended		6 Months Ended		29 Months Ended
	Mar. 31, 2018 USD ($)	Apr. 01, 2017 USD ($)	Mar. 31, 2018 USD ($)	Apr. 01, 2017 USD ($)	Mar. 31, 2018 USD ($) employee	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net	$ 114	$ 464	$ 219	$ 6,749	$ 84,700
Restructuring and Related Cost, Number of Positions Eliminated | employee					800
Headquarters relocation charges	1,000
Employee severance and related benefits
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net			(395)	2,861
Restructuring Reserve	243	8,976	243	8,976	$ 243	$ 1,736	$ 35,177
Facility closures and related costs
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net			(339)	3,888
Restructuring Reserve	3,316	4,173	3,316	4,173	3,316	4,508	1,431
Assumed Sublease Income	3,400		3,400		3,400
Total 2016 Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net			(734)	6,749
Restructuring Reserve	3,559	$ 13,149	3,559	$ 13,149	3,559	$ 6,244	$ 36,608
Accrued Expenses and Other Current Liabilities [Member] | Facility closures and related costs
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	1,900		1,900		1,900
Other Noncurrent Liabilities [Member] | Facility closures and related costs
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	$ 1,400		$ 1,400		$ 1,400