Income Taxes - Reconciliation of income tax and unrecognized tax benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Reconciliation of income tax computed at the U.S. federal statutory tax rate to income tax expense
Tax expense at U.S. statutory rate	$ 3,124	$ (3,877)	$ (9,252)
State income taxes, net of federal tax effect	(237)	(923)	(1,754)
Nondeductible expenses	1,186	(169)	7,765
Change in reserve for tax contingencies	(1,047)	(4,435)	27
Change in deferred tax asset valuation allowance	8,784	17,374	(5,382)
Foreign rate differential	5,684	9,912	(2,999)
Impact of US Tax Reform	(7,053)
Research and development credits	(2,656)	(3,459)	(2,542)
Other	(692)	235	(220)
Provision for income taxes	7,093	14,658	(14,357)
Compensation expense not expected to be deductible for tax purposes			6,300
Change in deferred tax asset valuation allowance, tax credit carryforwards	0	13,100
Tax charge from deferred taxes on unremitted foreign earnings	3,500	$ 9,500
Additional tax expenses relating to foreign earnings after enactment	2,100
Tax benefit due to remeasurement of deferred taxes	$ 7,100
Research tax credit			$ 1,000