ACCOUNTS PAYABLE AND ACCRUED LIABILITIES - Summary (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Accounts Payable and Accrued Liabilities [Abstract]
Funds held for customers	$ 392,375			$ 454,588
Compensation and benefits	266,967			117,739
Contract liabilities	193,405			146,947
Payment network fees	154,789			96,495
Trade accounts payable	148,084			76,229
Operating lease liabilities	88,812	$ 88,812	$ 37,339	0
Interest	61,296			1,671
Income taxes payable	56,426			51,108
Miscellaneous taxes and withholdings	48,738			15,436
Third-party processing fees	28,041			24,987
Unclaimed property	26,331			24,369
Audit and legal fees	26,080			7,543
Settlement of common share repurchases	17,200			4,000
Current portion of accrued buyout liability	14,817			14,011
Third-party commissions	13,641			24,998
Other	285,164			116,582
Accounts payable and accrued liabilities	1,822,166			1,176,703
Noncurrent accrued buyout liability	$ 34,200			$ 59,400

Accrued Buyout Liability, Current

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Accrued Buyout Liability, Noncurrent

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Accrued Fees and Assessment Expenses, Current

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Accrued Third Party Processing, Current

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Contract with Customer, Liability, Current, Customer Deposits

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Share Repurchase Accrual

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Unclaimed Property Liability

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Sum of the carrying values as of the balance sheet date of obligations incurred through that date and due within one year (or the operating cycle, if longer), including liabilities incurred (and for which invoices have typically been received) and payable to vendors for goods and services received, taxes, interest, rent and utilities, accrued salaries and bonuses, payroll taxes and fringe benefits.

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Carrying value as of the balance sheet date of obligations incurred (and for which invoices have typically been received) and payable to vendors for goods and services received that are used in an entity's business. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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Carrying value as of the balance sheet date of obligations incurred and payable for real and property taxes.

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Carrying value as of the balance sheet date of obligations incurred through that date and payable for professional fees, such as for legal and accounting services received. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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Carrying value as of the balance sheet date of obligations incurred through that date and payable for sales commissions. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable, classified as current.

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Total of the carrying values as of the balance sheet date of obligations incurred through that date and payable for obligations related to services received from employees, such as accrued salaries and bonuses, payroll taxes and fringe benefits. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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Carrying value as of the balance sheet date of [accrued] interest payable on all forms of debt, including trade payables, that has been incurred and is unpaid. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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Present value of lessee's discounted obligation for lease payments from operating lease, classified as current.

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Amount of expenses incurred but not yet paid classified as other, due within one year or the normal operating cycle, if longer.

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Carrying value as of the balance sheet date of obligations incurred and payable for statutory income, sales, use, payroll, excise, real, property and other taxes.

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