SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Revenues	$ 134,590	$ 90,385	$ 319,298	$ 267,132
IGS
Disaggregation of Revenue [Line Items]
Revenues	58,192	46,480	156,436	136,826
DHR
Disaggregation of Revenue [Line Items]
Revenues	21,716	23,076	65,172	70,158
Other
Disaggregation of Revenue [Line Items]
Revenues	17,050	15,626	47,083	46,393
Total transaction-based
Disaggregation of Revenue [Line Items]
Revenues	96,958	85,182	268,691	253,377
Development services
Disaggregation of Revenue [Line Items]
Revenues	10,329	2,463	18,369	7,284
Fixed-fee services
Disaggregation of Revenue [Line Items]
Revenues	27,303	2,740	32,238	6,471
State Enterprise
Disaggregation of Revenue [Line Items]
Revenues	91,475	73,257	243,690	217,981
State Enterprise | IGS
Disaggregation of Revenue [Line Items]
Revenues	58,192	46,480	156,436	136,826
State Enterprise | DHR
Disaggregation of Revenue [Line Items]
Revenues	21,716	23,076	65,172	70,158
State Enterprise | Other
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
State Enterprise | Total transaction-based
Disaggregation of Revenue [Line Items]
Revenues	79,908	69,556	221,608	206,984
State Enterprise | Development services
Disaggregation of Revenue [Line Items]
Revenues	10,329	2,463	18,369	7,284
State Enterprise | Fixed-fee services
Disaggregation of Revenue [Line Items]
Revenues	1,238	1,238	3,713	3,713
Payments
Disaggregation of Revenue [Line Items]
Revenues	11,266	9,736	30,996	28,973
Payments | IGS
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Payments | DHR
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Payments | Other
Disaggregation of Revenue [Line Items]
Revenues	11,266	9,736	30,996	28,973
Payments | Total transaction-based
Disaggregation of Revenue [Line Items]
Revenues	11,266	9,736	30,996	28,973
Payments | Development services
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Payments | Fixed-fee services
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
All Other
Disaggregation of Revenue [Line Items]
Revenues	31,849	7,392	44,612	20,178
All Other | IGS
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
All Other | DHR
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
All Other | Other
Disaggregation of Revenue [Line Items]
Revenues	5,784	5,890	16,087	17,420
All Other | Total transaction-based
Disaggregation of Revenue [Line Items]
Revenues	5,784	5,890	16,087	17,420
All Other | Development services
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
All Other | Fixed-fee services
Disaggregation of Revenue [Line Items]
Revenues	$ 26,065	$ 1,502	$ 28,525	$ 2,758