SIGNIFICANT ACCOUNTING POLICIES (income taxes, derivative financial instruments and revenue recognition) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income taxes
Measurement of tax benefit, minimum percentage tax benefit must be likely to be realized									50.00%
Derivative financial instruments
Net fair value of derivatives					$ 0					$ 0
Total revenue	$ 522,071	$ 493,593	$ 493,986	$ 499,065	$ 524,677	$ 493,190	$ 488,244	$ 491,914	$ 2,008,715	$ 1,998,025	$ 1,965,556
Deferred revenue, period over which recognized									1 year
Minimum [Member]
Capitalized contract costs amortization period									3 years
Maximum [Member]
Capitalized contract costs amortization period									5 years
Variable consideration [Member]
Variable consideration, period over which finalized									4 months
Total revenue									$ 200,000
Data-driven marketing and treasury management solutions [Member] | Minimum [Member]
Remaining performance obligations, expected timing of satisfaction	3 months								3 months
Data-driven marketing and treasury management solutions [Member] | Maximum [Member]
Remaining performance obligations, expected timing of satisfaction	1 year								1 year