Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 26, 2021	Mar. 27, 2020	Mar. 26, 2021	Mar. 27, 2020	Sep. 25, 2020
Income Tax Disclosure [Abstract]
Unrecognized tax benefits, gross	$ 66,900		$ 66,900		$ 60,700
Unrecognized tax benefits if recognized, would affect our effective tax rate	$ 44,600		44,600		$ 42,000
Effective tax rate (as a percent)	10.60%	20.00%		16.90%
Provision (benefit) for income taxes	$ (9,022)	$ (22,105)	$ (33,294)	$ (27,968)
Federal tax rate	21.00%