CUSTOMER FUNDS - Investments within Customer Funds Classified by Contractual Maturities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Amortized Cost
Due in one year or less	$ 490,299
Due in one to five years	533,853
Amortized Cost	1,024,152
Fair Value
Due in one year or less	492,456
Due in one to five years	537,303
Fair Value	1,029,759
Customer funds
Amortized Cost
Due in one year or less	237,909
Due in one to five years	0
Amortized Cost	237,909	$ 99,955
Fair Value
Due in one year or less	238,031
Due in one to five years	0
Fair Value	$ 238,031	$ 99,962