Segment and Geographic Information - Net Revenues based upon Source of Order by Geographic Area (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	$ 631,560	$ 527,499	$ 434,012
North America
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	233,243	174,432	157,426
UNITED STATES
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	232,700	172,900	156,900
Asia/Pacific
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	262,706	255,825	196,117
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	51,690	37,283	31,342
Rest of Europe
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	$ 83,921	$ 59,959	$ 49,127