Marketable Securities (Summary of Individual Securities In Continuous Unrealized Loss Position) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 24,286	$ 15,494
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(71)	(43)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	31,665	31,287
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(342)	(102)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	55,951	46,781
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	413	145
Certificates of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	219	240
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(1)	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	219	240
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	1	0
Corporate notes/bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	24,067	15,254
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(70)	(43)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	30,670	28,885
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(333)	(97)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	54,737	44,139
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	403	140
US Government Agencies Securities [Member]
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	995	2,402
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(9)	(5)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	995	2,402
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 9	$ 5