Income Taxes - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Operating Loss Carryforwards [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%	24.50%
Income Tax Holiday, Aggregate Dollar Amount	$ 8,200	$ 8,100	$ 6,400
Income Tax Holiday, Income Tax Benefits Per Share	$ 0.13	$ 0.13	$ 0.10
Deferred Tax Assets, Operating Loss Carryforwards	$ 54,842	$ 12,269
Deferred Tax Assets, Tax Credit Carryforwards	15,807	13,783
Valuation Allowance, Deferred Tax Asset, Change in Amount	9,100	700
Unrecognized Tax Benefits	51,767	42,287	$ 31,672	$ 23,135
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	34,300	29,400	23,100
Unrecognized Tax Benefits, Period Increase (Decrease)	(1,000)	2,400	$ 400
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	3,000	$ 4,000
Foreign [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carry-forwards, net	59,500
Deferred Tax Assets, Operating Loss Carryforwards, Subject to Expiration	3,400
Deferred Tax Assets, Tax Credit Carryforwards	4,000
Domestic Tax Authority [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carry-forwards, net	111,800
Deferred Tax Assets, Operating Loss Carryforwards, Subject to Expiration	58,900
Deferred Tax Assets, Operating Loss Carryforwards	170,700
Deferred Tax Assets, Tax Credit Carryforwards	500
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carry-forwards, net	158,200
Deferred Tax Assets, Operating Loss Carryforwards, Subject to Expiration	221,400
Deferred Tax Assets, Operating Loss Carryforwards	379,600
Deferred Tax Assets, Tax Credit Carryforwards	15,600
Deferred Tax Assets, Tax Credit Carryforwards, Subject to Expiration	$ 3,700