Marketable Securities - General Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Schedule of Available-for-sale Securities [Line Items]
Marketable securities sold during period, fair value		$ 2,500
Sales of marketable securities	$ 25	2,492	$ 48,903
Maximum
Schedule of Available-for-sale Securities [Line Items]
Net realized gain, (loss)		100
Reclassification unrealized net holding gain, (loss)		$ 100