SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)	12 Months Ended
	Dec. 31, 2021 USD ($) store businessDay segment	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jan. 01, 2022 USD ($)
Significant Accounting Policies [Line Items]
Losses, uninsured amount	$ 0
Losses, uninsured amount on foreign bank accounts	0
Write off from financial institution closure	2,000,000
Advertising costs	2,500,000	$ 400,000	$ 1,200,000
Gains (losses) from foreign currency transactions	$ 300,000	200,000	$ 41,000
Foreign currency transactions, settlement, threshold business days | businessDay	2
Amount of foreign exchange contracts opened	$ 48,600,000	42,500,000
Wire transfers payable, net in in foreign currencies	17,800,000	7,600,000
Prepaid wires, net in in foreign currencies	$ 39,700,000	$ 50,100,000
Number of reportable segments | segment	1
Number of company-operated stores | store	36
Subsequent Event
Significant Accounting Policies [Line Items]
Opearting lease, right-of-use asset				$ 5,600,000
Operating lease liability				$ 5,600,000
Maximum
Significant Accounting Policies [Line Items]
Number of days recorded upon initiation of wire transfer	5 days
Threshold period past due for write-off of accounts receivable	90 days
Agent relationships
Significant Accounting Policies [Line Items]
Intangible assets, estimated useful life	15 years
Trade name
Significant Accounting Policies [Line Items]
Intangible assets, estimated useful life	15 years
Developed technology
Significant Accounting Policies [Line Items]
Intangible assets, estimated useful life	15 years
Other intangibles
Significant Accounting Policies [Line Items]
Intangible assets, estimated useful life	10 years
Computer Equipment
Significant Accounting Policies [Line Items]
Property and equipment, estimated useful life	5 years
Remittance Volume | Paying Agent Concentration Risk | Banking, Financial Services, and Retail
Significant Accounting Policies [Line Items]
Concentration risk percentage	22.00%	18.00%