Marketable Securities - General Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Marketable securities sold during period, fair value	$ 0	$ 49,400
Marketable securities sold during period, amortized cost basis		49,500
Net realized losses		100
Sales of marketable securities		48,904
Reclassification unrealized net holding losses		$ 100