Revenue Recognition - Disaggregation of Revenues (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	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Revenue	$ 25,018	$ 21,906	$ 19,983	$ 17,683	$ 21,037	$ 16,109	$ 14,277	$ 12,136	$ 12,904	$ 11,798	$ 11,419	$ 9,269	$ 84,590	$ 63,559	$ 45,390
Deposits revenue
Disaggregation of Revenue [Line Items]
Revenue													57,030	41,508	32,370
Deposits software and hardware | Transferred at point in time
Disaggregation of Revenue [Line Items]
Revenue													41,860	33,071	25,407
Deposits service and other | Transferred over time
Disaggregation of Revenue [Line Items]
Revenue													15,170	8,437	6,963
Identity verification revenue
Disaggregation of Revenue [Line Items]
Revenue													27,560	22,051	13,020
Identity verification software and hardware | Transferred at point in time
Disaggregation of Revenue [Line Items]
Revenue													4,985	7,627	4,240
Identity verification service and other | Transferred over time
Disaggregation of Revenue [Line Items]
Revenue													$ 22,575	$ 14,424	$ 8,780