Geographic Regions (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenue	$ 28,832	$ 41,200	$ 32,783	$ 73,611	$ 54,677	$ 47,760	$ 32,944	$ 29,135	$ 176,426	$ 164,516	$ 120,308
Operating income (loss)	(8,848)	$ 2,936	$ 65	$ 7,766	8,034	$ 3,971	$ (1,400)	$ (180)	1,919	10,425	(7,908)
Net long-lived assets	16,452				15,792				16,452	15,792
The Netherlands
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenue									76,373	81,443	52,189
Operating income (loss)									(5,269)	5,206	(7,773)
Net long-lived assets	5,943				5,190				5,943	5,190
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenue									72,753	60,952	44,299
Operating income (loss)									3,871	1,527	(1,396)
Net long-lived assets	10,039				9,924				10,039	9,924
France
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenue									6,129	5,588	8,758
Operating income (loss)									(3,058)	(1,000)	(783)
Net long-lived assets	177				289				177	289
China
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenue									17,634	12,673	11,799
Operating income (loss)									5,445	3,647	1,530
Net long-lived assets	$ 293				$ 389				293	389
Other
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenue									3,537	3,860	3,263
Operating income (loss)									$ 930	$ 1,045	$ 514