Reportable Segments, Geographic Information and Major Customers - Narrative (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018 USD ($)	Sep. 28, 2019 USD ($) segment	Sep. 29, 2018 USD ($)	Sep. 30, 2017 USD ($)
Segment Reporting [Abstract]
Restructuring costs		$ 1,678	$ 0	$ 0
One-time employee bonus	$ 13,500		13,500
Number of reportable segments | segment		3
Other long-term assets and deferred income tax assets		$ 78,400	$ 74,200
Customer Concentration Risk | General Electric Company (GE) | Accounts Receivable
Concentration Risk [Line Items]
Percentage of concentration risk		10.10%	10.90%