Earnings Per Share - Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended								9 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	Jun. 25, 2018	Sep. 30, 2020		Sep. 30, 2019		Sep. 30, 2018
Numerator
Net (loss) income attributable to Class A common stockholders		$ (651)	$ (356)	$ 737	$ (149)	$ (930)	$ (1,191)	$ (1,102)	$ 178	$ (7,634)	$ (419)		$ (3,045)		$ (6,898)
Denominator
Weighted average shares of Class A common stock outstanding - diluted (shares)	[1]										27,429,801		10,490,981		26,873,878
Diluted net (loss) income per share (in USD per share)		$ (0.06)	$ (0.02)	$ 0.05	$ (0.01)	$ (0.07)	$ (0.12)	$ (0.12)	$ 0.02		$ (0.03)	[2]	$ (0.29)	[2]	$ 0.08	[2]
Class A Common Stock
Numerator
Net (loss) income attributable to Class A common stockholders											$ (419)		$ (3,045)		$ 736
Reallocation of net (loss) income assuming conversion of common units											(422)				1,464
Net (loss) income attributable to Class A common stockholders - diluted											$ (841)				$ 2,200
Denominator
Weighted average shares of Class A common stock outstanding (shares)											14,833,378		10,490,981		8,812,630
Weighted average effect of dilutive securities (shares)											12,596,423				18,061,248
Weighted average shares of Class A common stock outstanding - diluted (shares)											27,429,801				26,873,878
Diluted net (loss) income per share (in USD per share)															$ 0.08

[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.

[2] Basic and diluted net income per share of Class A common stock are presented only for the period after the Company’s Reorganization Transactions. See Note 1 for a description of the Reorganization Transactions. See Note 18 for the calculation of income per common share.