CUSTOMER FUNDS - Contractual Maturities of Investments within Customer Funds (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Amortized Cost
Due in one year or less	$ 520,017
Due in one to five years	528,798
Amortized Cost	1,048,815
Fair Value
Due in one year or less	521,840
Due in one to five years	529,460
Fair Value	1,051,300
Customer funds
Amortized Cost
Due in one year or less	295,500
Due in one to five years	0
Amortized Cost	295,500	$ 237,909
Fair Value
Due in one year or less	296,351
Due in one to five years	0
Fair Value	$ 296,351	$ 238,031