Stock-based Compensation (Narrative) (Details)	3 Months Ended		6 Months Ended
	Mar. 31, 2018 USD ($) shares / unit	Apr. 01, 2017 USD ($)	Mar. 31, 2018 USD ($) shares / unit	Apr. 01, 2017 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Common Stock Issuable per Restricted Stock Unit | shares / unit	1		1
ESPP maximum contribution percentage	10.00%		10.00%
ESPP maximum contribution amount by employee			$ 25,000
ESPP purchase price as a % of stock price	85.00%		85.00%
Stock-based compensation	$ 17,026,000	$ 21,577,000	$ 35,357,000	$ 39,565,000
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 1,000,000	$ 700,000	$ 2,100,000	$ 1,300,000