Marketable Securities - General Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Schedule of Available-for-sale Securities [Line Items]
Marketable securities sold during period, fair value	$ 0		$ 2,500	$ 49,400
Marketable securities sold during period, amortized cost basis	0		2,500	49,500
Net realized gain, (loss)				(100)
Sales of marketable securities	2,500	$ 0	2,492	48,904
Reclassification unrealized net holding gain, (loss)				$ (100)
Maximum
Schedule of Available-for-sale Securities [Line Items]
Net realized gain, (loss)			100
Reclassification unrealized net holding gain, (loss)	$ 100		$ 100