Marketable Securities (Schedule of Fair Value and Gross Unrealized Losses) (Details) - Corporate notes/bonds - USD ($) $ in Thousands	Dec. 28, 2019	Sep. 30, 2019
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 17,718	$ 12,419
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(13)	(14)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	12,814	16,369
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(6)	(14)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	30,532	28,788
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (19)	$ (28)