Income Taxes Gross Unrecognized Tax Benefits Rollforward (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Tax cuts and jobs act of 2017, change in tax rate, deferred tax liability, income tax (expense) benefit		$ 3,641
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance as of beginning of period	$ 1,075	0	$ 0
Tax positions related to the current year	0	0	0
Tax positions related to prior years	0	1,075	0
Reductions	(25)	0	0
Expiration of statutes of limitations	0	0	0
Balance as of end of period	$ 1,050	$ 1,075	$ 0