Income Taxes - Reconciliation of income tax and unrecognized tax benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Reconciliation of income tax computed at the U.S. federal statutory tax rate to income tax expense
Tax expense at U.S. statutory rate	$ 10,992	$ 3,124	$ (3,877)
State income taxes, net of federal tax effect	1,416	(237)	(923)
Nondeductible expenses	1,720	1,186	(185)
Change in reserve for tax contingencies	(1,468)	(1,047)	(4,435)
Change in deferred tax asset valuation allowance	(10,007)	8,784	17,374
Foreign rate differential	2,149	5,684	9,912
Tax credits	(4,767)	(2,656)	(3,459)
Impact of U.S. Tax Reform		(7,053)
Global Intangible Low-Tax Income	8,182
Stock Based Compensation	(448)	59	16
Non-controlling interest in equity arrangements	1,802	99
Other	1,469	(850)	235
Provision for income taxes	$ 11,040	7,093	14,658
Tax charge from deferred taxes on unremitted foreign earnings		3,500	$ 9,500
Additional tax expenses relating to foreign earnings after enactment		$ 2,100