CUSTOMER FUNDS - Investments within Customer Funds (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 1,024,152
Fair Value	1,029,759
Customer funds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	237,909	$ 99,955
Gross Unrealized Gains	144	14
Gross Unrealized Losses	(22)	(7)
Fair Value	238,031	99,962
Customer funds \| U.S. agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		27,293
Gross Unrealized Gains		2
Gross Unrealized Losses		(4)
Fair Value		27,291
Customer funds \| U.S. government securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	237,909	72,662
Gross Unrealized Gains	144	12
Gross Unrealized Losses	(22)	(3)
Fair Value	$ 238,031	$ 72,671

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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