Summary of Significant Accounting Policies - Disaggregated Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Total revenue	$ 41,111	$ 84,868
Revenue Transferred over Time
Disaggregation of Revenue [Line Items]
Total revenue	27,671	74,940
Revenue Transferred at a Point in Time
Disaggregation of Revenue [Line Items]
Total revenue	13,440	9,928
Payments Revenue
Disaggregation of Revenue [Line Items]
Total revenue	28,371	77,739
Other Revenue
Disaggregation of Revenue [Line Items]
Total revenue	12,740	7,129
Merchant Services
Disaggregation of Revenue [Line Items]
Total revenue	27,465	77,702
Merchant Services | Revenue Transferred over Time
Disaggregation of Revenue [Line Items]
Total revenue	18,130	68,948
Merchant Services | Revenue Transferred at a Point in Time
Disaggregation of Revenue [Line Items]
Total revenue	9,335	8,754
Merchant Services | Payments Revenue
Disaggregation of Revenue [Line Items]
Total revenue	22,453	72,537
Merchant Services | Other Revenue
Disaggregation of Revenue [Line Items]
Total revenue	5,012	5,165
Proprietary Software and Payments
Disaggregation of Revenue [Line Items]
Total revenue	14,056	7,166
Proprietary Software and Payments | Revenue Transferred over Time
Disaggregation of Revenue [Line Items]
Total revenue	9,949	5,992
Proprietary Software and Payments | Revenue Transferred at a Point in Time
Disaggregation of Revenue [Line Items]
Total revenue	4,107	1,174
Proprietary Software and Payments | Payments Revenue
Disaggregation of Revenue [Line Items]
Total revenue	6,326	5,202
Proprietary Software and Payments | Other Revenue
Disaggregation of Revenue [Line Items]
Total revenue	7,730	1,964
Other
Disaggregation of Revenue [Line Items]
Total revenue	(410)	0
Other | Revenue Transferred over Time
Disaggregation of Revenue [Line Items]
Total revenue	(408)	0
Other | Revenue Transferred at a Point in Time
Disaggregation of Revenue [Line Items]
Total revenue	(2)	0
Other | Payments Revenue
Disaggregation of Revenue [Line Items]
Total revenue	(408)	0
Other | Other Revenue
Disaggregation of Revenue [Line Items]
Total revenue	$ (2)	$ 0