INCOME TAXES - NARRATIVE (Details) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2017	Dec. 31, 2016
Income Tax Contingency [Line Items]
Unrecognized tax benefits that would impact the ETR	$ 107,400,000	$ 107,400,000	$ 102,900,000
Unrecognized tax benefits, increase resulting from current period tax positions	1,900,000	5,700,000
Unrecognized tax benefits, from foreign currency fluctuations	1,000,000	3,700,000
Unrecognized tax benefits, reduction due to expirations of statute of limitations	400,000	400,000
Unrecognized tax benefits, income tax penalties and interest accrued	28,900,000	28,900,000	$ 24,300,000
Ghana Revenue Authority
Income Tax Contingency [Line Items]
Benefit to income tax expense		11,600,000
Minimum
Income Tax Contingency [Line Items]
Decrease in unrecognized tax benefits is reasonably possible	0	0
Maximum
Income Tax Contingency [Line Items]
Decrease in unrecognized tax benefits is reasonably possible	$ 11,500,000	$ 11,500,000