SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Revenues	$ 93,589	$ 91,566	$ 184,708	$ 176,747
IGS
Disaggregation of Revenue [Line Items]
Revenues	50,055	47,595	98,243	90,347
DHR
Disaggregation of Revenue [Line Items]
Revenues	20,607	23,396	43,456	47,081
Other
Disaggregation of Revenue [Line Items]
Revenues	14,551	15,880	30,033	30,766
Total transaction-based
Disaggregation of Revenue [Line Items]
Revenues	85,213	86,871	171,732	168,194
Development services
Disaggregation of Revenue [Line Items]
Revenues	5,904	2,642	8,041	4,821
Fixed-fee services
Disaggregation of Revenue [Line Items]
Revenues	2,472	2,053	4,935	3,732
State Enterprise
Disaggregation of Revenue [Line Items]
Revenues	77,804	74,871	152,215	144,724
State Enterprise | IGS
Disaggregation of Revenue [Line Items]
Revenues	50,055	47,595	98,243	90,347
State Enterprise | DHR
Disaggregation of Revenue [Line Items]
Revenues	20,607	23,396	43,456	47,081
State Enterprise | Other
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
State Enterprise | Total transaction-based
Disaggregation of Revenue [Line Items]
Revenues	70,662	70,991	141,699	137,428
State Enterprise | Development services
Disaggregation of Revenue [Line Items]
Revenues	5,904	2,642	8,041	4,821
State Enterprise | Fixed-fee services
Disaggregation of Revenue [Line Items]
Revenues	1,238	1,238	2,475	2,475
Payments
Disaggregation of Revenue [Line Items]
Revenues	9,713	9,884	19,729	19,237
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	9,713	9,884	19,729	19,237
Payments | Total transaction-based
Disaggregation of Revenue [Line Items]
Revenues	9,713	9,884	19,729	19,237
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	6,072	6,811	12,764	12,786
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	4,838	5,996	10,304	11,529
All Other | Total transaction-based
Disaggregation of Revenue [Line Items]
Revenues	4,838	5,996	10,304	11,529
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	$ 1,234	$ 815	$ 2,460	$ 1,257