CUSTOMER FUNDS - Assets Underlying Customer Funds (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Customer funds	$ 3,190,905	$ 2,830,995
U.S. agency securities
Debt Securities, Available-for-sale [Line Items]
Customer funds	0	29,994
U.S. government securities
Debt Securities, Available-for-sale [Line Items]
Customer funds	0	360,060
Cash
Debt Securities, Available-for-sale [Line Items]
Customer funds	2,332,936	242,243
Cash Equivalents | Money market funds
Debt Securities, Available-for-sale [Line Items]
Customer funds	187,782	2,126,579
Cash Equivalents | Reverse repurchase agreement
Debt Securities, Available-for-sale [Line Items]
Customer funds	$ 670,187	$ 72,119