Marketable Securities - General Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Marketable securities sold during period, fair value	$ 49,400	$ 0
Marketable securities sold during period, amortized cost basis	49,500	$ 0
Net realized losses	100
Sales of marketable securities	48,904
Reclassification unrealized net holding losses	$ 100