Income Taxes - Reconciliation of income tax and unrecognized tax benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Reconciliation of income tax computed at the U.S. federal statutory tax rate to income tax expense
Tax expense (benefit) at U.S. statutory rate	$ (721)	$ 10,992	$ 3,124
State income taxes, net of federal tax effect	(1,879)	1,416	(237)
Base Erosion and Anti-abuse Tax	3,148	540
Global Intangible Low-Tax Income	7,387	8,182
Foreign rate differential	(494)	2,149	5,684
Nondeductible expenses	652	4	1,020
Stock based compensation	1,056	438	226
Acquisition related Items	(704)	831	166
Tax credits	(3,962)	(4,767)	(2,656)
Reserve for tax contingencies	(575)	(1,468)	(1,047)
Deferred tax asset valuation allowance	(9,017)	(10,007)	8,784
Impact of U.S. Tax Reform			(7,053)
Non-controlling interest in equity arrangements	(967)	1,802	99
Other	(304)	928	(1,017)
Provision (benefit) for income taxes	$ (6,380)	$ 11,040	$ 7,093