Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	[1]	Jun. 30, 2018	[1]	Mar. 31, 2018	[1]	Dec. 31, 2017	[1]	Sep. 30, 2019	Sep. 30, 2018	[1]	Sep. 30, 2017	[1]
Disaggregation of Revenue [Line Items]
Total revenues	$ 64,960	$ 61,166	$ 65,764	$ 62,313	$ 65,118		$ 62,272		$ 54,548		$ 44,955		$ 254,203	$ 226,893		$ 181,340
North America, primarily United States
Disaggregation of Revenue [Line Items]
Total revenues													184,022	161,924		117,455
Europe, Middle East & Africa
Disaggregation of Revenue [Line Items]
Total revenues													39,896	39,211		39,403
Rest of world
Disaggregation of Revenue [Line Items]
Total revenues													30,285	25,758		24,482
Transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenues													231,387	212,448		176,567
Transferred over time
Disaggregation of Revenue [Line Items]
Total revenues													$ 22,816	$ 14,445		$ 4,773

[1] Prior period information has been restated for the adoption of ASU No. 2014-09, “Revenue from Contracts with Customers (Topic 606)”, which we adopted on October 1, 2018.