Marketable Securities (Details) $ in Thousands	3 Months Ended
	Dec. 31, 2017 USD ($) Security	Dec. 31, 2016 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Number of securities below amortized cost basis	31
Number of securities	41
Proceeds from maturities and sales of marketable securities | $	$ 4,296	$ 32,155
Current Assets
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, next twelve months, maximum year mature	1 year
Non-current Assets
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, year two through five, maximum year mature	2 years