Marketable Securities - General Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Investments, Debt and Equity Securities [Abstract]
Marketable securities sold during period, fair value	$ 49,400	$ 1,600
Marketable securities sold during period, amortized cost basis	49,500	1,600
Net realized losses	100
Sales of marketable securities	48,903	1,584	$ 3,590
Reclassification unrealized net holding losses	$ 100	$ 100