Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Total revenues	$ 73,169	$ 70,338	$ 73,447	$ 62,317	$ 64,960	$ 61,166	$ 65,764	$ 62,313	$ 279,271	$ 254,203	$ 226,893
North America, primarily United States
Disaggregation of Revenue [Line Items]
Total revenues									213,487	184,022	161,924
Europe, Middle East & Africa
Disaggregation of Revenue [Line Items]
Total revenues									40,076	39,896	39,211
Rest of world
Disaggregation of Revenue [Line Items]
Total revenues									25,708	30,285	25,758
Transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenues									253,371	231,387	212,448
Transferred over time
Disaggregation of Revenue [Line Items]
Total revenues									$ 25,900	$ 22,816	$ 14,445