Marketable Securities (Fair Value and Gross Unrealized Losses for AFS) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Sep. 30, 2014
Schedule of Available-for-sale Securities [Line Items]
Fair value of available-for-sale securities in continuous unrealized loss position for less than twelve months	$ 29,720	$ 30,453
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(49)	(47)
Fair value of available-for-sale securities in continuous unrealized loss position for twelve months or longer	5,002	748
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(1)	(2)
Corporate Bonds
Schedule of Available-for-sale Securities [Line Items]
Fair value of available-for-sale securities in continuous unrealized loss position for less than twelve months	26,499	23,475
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(44)	(26)
Fair value of available-for-sale securities in continuous unrealized loss position for twelve months or longer	5,002	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(1)	0
Commercial Paper
Schedule of Available-for-sale Securities [Line Items]
Fair value of available-for-sale securities in continuous unrealized loss position for less than twelve months	1,991	3,998
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(4)	(1)
Fair value of available-for-sale securities in continuous unrealized loss position for twelve months or longer	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Certificates of Deposit
Schedule of Available-for-sale Securities [Line Items]
Fair value of available-for-sale securities in continuous unrealized loss position for less than twelve months		2,980
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		(20)
Fair value of available-for-sale securities in continuous unrealized loss position for twelve months or longer		748
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		$ (2)
Government municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Fair value of available-for-sale securities in continuous unrealized loss position for less than twelve months	1,230
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(1)
Fair value of available-for-sale securities in continuous unrealized loss position for twelve months or longer	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 0