Income Taxes - Provision for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Federal statutory rate	21.00%	21.00%	21.00%
U.S. benefits from research and experimentation activities	3.40%	(1.50%)	(2.90%)
State taxes, net of federal effect	1.20%	1.10%	(4.70%)
Foreign income at other than U.S. rates	(11.60%)	1.70%	10.30%
Excess compensation	(3.30%)	0.40%	6.40%
Share-based compensation	7.40%	(2.20%)	(7.20%)
U.S. tax reform	0	0	0.141
Global Intangible Low Taxed Income ("GILTI")	1.50%	0.00%	3.10%
Foreign derived intangible income	14.40%	(3.40%)	(3.90%)
Change in reserve positions	(11.10%)	1.90%	0.30%
Goodwill impairment	(47.50%)	0.00%	0.00%
Other, net	(0.60%)	(1.40%)	1.40%
Provision for income taxes	(25.20%)	17.60%	37.90%
Loss before taxes	$ 54,794	$ (173,347)	$ (63,106)