Revenue Recognition - Disaggregation of Revenues (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, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Revenue	$ 30,638	$ 25,413	$ 23,192	$ 22,067	$ 25,018	$ 21,906	$ 19,983	$ 17,683	$ 21,037	$ 16,109	$ 14,277	$ 12,136	$ 101,310	$ 84,590	$ 63,559
Deposits revenue
Disaggregation of Revenue [Line Items]
Revenue													67,730	57,030	41,508
Deposits software and hardware | Transferred at point in time
Disaggregation of Revenue [Line Items]
Revenue													49,765	41,860	33,071
Deposits services and other | Transferred over time
Disaggregation of Revenue [Line Items]
Revenue													17,965	15,170	8,437
Identity verification revenue
Disaggregation of Revenue [Line Items]
Revenue													33,580	27,560	22,051
Identity verification software and hardware | Transferred at point in time
Disaggregation of Revenue [Line Items]
Revenue													4,387	4,985	7,627
Identity verification services and other | Transferred over time
Disaggregation of Revenue [Line Items]
Revenue													$ 29,193	$ 22,575	$ 14,424