SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Disaggregation of Revenue [Line Items]
Revenues	$ 91,119	$ 85,180
IGS
Disaggregation of Revenue [Line Items]
Revenues	48,187	42,751
DHR
Disaggregation of Revenue [Line Items]
Revenues	22,849	23,685
Other
Disaggregation of Revenue [Line Items]
Revenues	15,480	14,886
Total transaction-based
Disaggregation of Revenue [Line Items]
Revenues	86,516	81,322
Development services
Disaggregation of Revenue [Line Items]
Revenues	2,137	2,179
Fixed-fee services
Disaggregation of Revenue [Line Items]
Revenues	2,466	1,679
State Enterprise
Disaggregation of Revenue [Line Items]
Revenues	74,411	69,853
State Enterprise | IGS
Disaggregation of Revenue [Line Items]
Revenues	48,187	42,751
State Enterprise | DHR
Disaggregation of Revenue [Line Items]
Revenues	22,849	23,685
State Enterprise | Other
Disaggregation of Revenue [Line Items]
Revenues	0	0
State Enterprise | Total transaction-based
Disaggregation of Revenue [Line Items]
Revenues	71,036	66,436
State Enterprise | Development services
Disaggregation of Revenue [Line Items]
Revenues	2,137	2,179
State Enterprise | Fixed-fee services
Disaggregation of Revenue [Line Items]
Revenues	1,238	1,238
Payments
Disaggregation of Revenue [Line Items]
Revenues	10,016	9,352
Payments | IGS
Disaggregation of Revenue [Line Items]
Revenues	0	0
Payments | DHR
Disaggregation of Revenue [Line Items]
Revenues	0	0
Payments | Other
Disaggregation of Revenue [Line Items]
Revenues	10,016	9,352
Payments | Total transaction-based
Disaggregation of Revenue [Line Items]
Revenues	10,016	9,352
Payments | Development services
Disaggregation of Revenue [Line Items]
Revenues	0	0
Payments | Fixed-fee services
Disaggregation of Revenue [Line Items]
Revenues	0	0
All Other
Disaggregation of Revenue [Line Items]
Revenues	6,692	5,975
All Other | IGS
Disaggregation of Revenue [Line Items]
Revenues	0	0
All Other | DHR
Disaggregation of Revenue [Line Items]
Revenues	0	0
All Other | Other
Disaggregation of Revenue [Line Items]
Revenues	5,464	5,534
All Other | Total transaction-based
Disaggregation of Revenue [Line Items]
Revenues	5,464	5,534
All Other | Development services
Disaggregation of Revenue [Line Items]
Revenues	0	0
All Other | Fixed-fee services
Disaggregation of Revenue [Line Items]
Revenues	$ 1,228	$ 441