CUSTOMER FUNDS - Investments within Customer Funds (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 1,048,815
Fair Value	1,051,300
Customer funds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	295,500	$ 237,909
Gross Unrealized Gains	921	144
Gross Unrealized Losses	(70)	(22)
Fair Value	296,351	238,031
Customer funds \| U.S. agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	118,750
Gross Unrealized Gains	100
Gross Unrealized Losses	(15)
Fair Value	118,835
Customer funds \| U.S. government securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	176,750	237,909
Gross Unrealized Gains	821	144
Gross Unrealized Losses	(55)	(22)
Fair Value	$ 177,516	$ 238,031

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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