Marketable Securities (Schedule of available-for-sale marketable securities by contractual maturity date) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017
Investments, Debt and Equity Securities [Abstract]
Available-for-sale Securities, Debt Maturities, Next Rolling Twelve Months, Amortized Cost Basis	$ 25,792	$ 18,274
Available-for-sale Securities, Debt Maturities, Next Rolling Twelve Months, Fair Value	25,670	18,244
Available-for-sale Securities, Debt Maturities, Rolling Year Two Through Five, Amortized Cost Basis	30,572	32,184
Available-for-sale Securities, Debt Maturities, Rolling Year Two Through Five, Fair Value	30,281	32,071
Available-for-sale Debt Securities, Amortized Cost Basis	56,364	50,458
Available-for-sale Securities, Debt Securities	$ 55,951	$ 50,315