Marketable Securities (Schedule of Available-for-sale Marketable Securities by Contractual Maturity Date) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Sep. 30, 2017
Investments, Debt and Equity Securities [Abstract]
Due in one year or less, amortized cost	$ 22,300	$ 18,274
Due in one year or less, fair value	22,170	18,244
Due after one year through three years, amortized cost	32,395	32,184
Due after one year through three years, fair value	32,002	32,071
Amortized cost	54,695	50,458
Fair value	$ 54,172	$ 50,315