SEGMENT AND GEOGRAPHICAL INFORMATION - Reconciliation of Total Segment Profit to Income before applicable Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segment gross profit	$ 963,501	$ 538,501
Less: Product development	308,678	194,986
Less: Sales and marketing	349,460	194,535
Less: General and administrative	195,909	129,495
Less: Transaction and loan losses	20,395	108,883
Less: Bitcoin impairment losses	19,860	0
Less: Amortization of acquired customer assets	6,884	4,152
Less: Interest expense, net	253	9,206
Less: Other expense, net	27,528	5,862
Income (loss) before income tax	39,955	(105,356)
Customer assets
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Less: Amortization of acquired customer assets	1,463	890
Operating Segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segment gross profit	$ 963,501	$ 538,501