Segments (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
Segment Reporting Information [Line Items]
Revenue	$ 38,272	$ 31,573	$ 39,178	$ 41,111	$ 108,562	$ 97,483	$ 85,394	$ 84,868	$ 150,134	$ 376,307		$ 323,508
Operating expenses
Interchange and network fees									0	242,867	[1]	214,543	[1]
Other costs of services									47,230	44,237		40,314
Selling general and administrative									78,323	62,860		40,585
Depreciation and amortization									18,217	16,564		11,839
Change in fair value of contingent consideration									(1,409)	3,389		3,866
Income from operations	1,198	$ 437	$ 2,041	$ 4,097	1,869	$ 1,194	$ (203)	$ 3,530	7,773	6,390		12,361
Processing margin									123,352	106,866		83,180
Total assets	403,526				349,302				403,526	349,302		175,142
Goodwill	187,005				168,284				187,005	168,284		83,954
Merchant Services
Segment Reporting Information [Line Items]
Revenue									100,949	338,968		303,692
Operating expenses
Interchange and network fees										236,170		209,705
Other costs of services									43,940	41,487		38,563
Selling general and administrative									26,376	27,275		23,716
Depreciation and amortization									11,796	12,221		9,736
Change in fair value of contingent consideration									(4,691)	(477)		2,103
Income from operations									23,528	22,292		19,869
Processing margin									78,627	78,369		69,449
Total assets	206,769				216,420				206,769	216,420		143,792
Goodwill	115,982				117,334				115,982	117,334		70,936
Residual expense									21,618	17,058		14,025
Proprietary Software and Payments
Segment Reporting Information [Line Items]
Revenue									50,953	37,339		19,819
Operating expenses
Interchange and network fees										6,697		4,838
Other costs of services									5,057	2,750		1,752
Selling general and administrative									28,187	17,059		7,177
Depreciation and amortization									5,723	3,790		1,896
Change in fair value of contingent consideration									3,282	3,866		1,763
Income from operations									8,704	3,177		2,393
Processing margin									46,483	28,497		13,733
Total assets	139,107				99,420				139,107	99,420		26,524
Goodwill	71,023				50,950				71,023	50,950		13,018
Residual expense									587	605		504
Other
Segment Reporting Information [Line Items]
Revenue									(1,768)	0		(3)
Operating expenses
Interchange and network fees										0		0
Other costs of services									(1,767)	0		(1)
Selling general and administrative									23,760	18,526		9,692
Depreciation and amortization									698	553		207
Change in fair value of contingent consideration									0	0		0
Income from operations									(24,459)	(19,079)		(9,901)
Processing margin									(1,758)	0		(2)
Total assets	57,650				33,462				57,650	33,462		4,826
Goodwill	$ 0				$ 0				0	0		0
Residual expense									$ (1,757)	$ 0		$ 0

[1] Effective October 1, 2019, the Company's revenues are presented net of interchange and network fees in accordance with Accounting Standards Codification Topic 606, Revenue from Contracts with Customers. See Note 2 to our consolidated financial statements for a description of the recently adopted accounting pronouncement.