Marketable Securities (Schedule of Fair Value and Gross Unrealized Losses) (Details) - USD ($) $ in Thousands	Mar. 30, 2019	Sep. 30, 2018
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 10,810	$ 24,286
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(15)	(71)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	27,785	31,665
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(146)	(342)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	38,595	55,951
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(161)	(413)
Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		219
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		(1)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		219
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		(1)
Corporate notes/bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	10,810	24,067
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(15)	(70)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	26,784	30,670
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(144)	(333)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	37,594	54,737
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(159)	(403)
U.S. government agency securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	1,001	995
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(2)	(9)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	1,001	995
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (2)	$ (9)