GOODWILL AND INTANGIBLE ASSETS - Intangible Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	$ 305,823	$ 304,875
Intangible assets, accumulated amortization	(130,520)	(122,049)
Intangible assets, net	175,303	182,826
Merchant portfolios
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	115,502	114,554
Intangible assets, accumulated amortization	(16,107)	(12,655)
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	40,740	40,740
Intangible assets, accumulated amortization	(26,818)	(25,836)
Residual buyouts
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	112,731	112,731
Intangible assets, accumulated amortization	(62,895)	(59,796)
Non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	3,390	3,390
Intangible assets, accumulated amortization	(3,390)	(3,390)
Trade names
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	2,870	2,870
Intangible assets, accumulated amortization	(1,331)	(1,273)
Technology
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	15,390	15,390
Intangible assets, accumulated amortization	(13,387)	(12,758)
ISO relationships
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	15,200	15,200
Intangible assets, accumulated amortization	$ (6,592)	$ (6,341)