STOCK-BASED COMPENSATION AND EMPLOYEE BENEFIT PLANS - Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 7,158	$ 6,769	$ 6,338
Cost of revenues | State enterprise cost of revenues, exclusive of depreciation & amortization
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	1,585	1,499	1,516
Cost of revenues | Software & services cost of revenues, exclusive of depreciation & amortization
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	162	101	151
Selling & administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	4,599	4,495	3,994
Enterprise technology & product support
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 812	$ 674	$ 677