SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Comprehensive Income (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2017 USD ($)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at the beginning of the period	$ (346,359)
Balance at the end of the period	(288,102)
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at the beginning of the period	(251,228)
Current-period comprehensive income (loss)	60,017
Balance at the end of the period	(191,211)
Gain/(Loss) on Hedging Activities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at the beginning of the period	7,978
Current-period comprehensive income (loss)	(1,760)
Balance at the end of the period	6,218
Defined Benefit Pension Plan
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at the beginning of the period	(103,109)
Current-period comprehensive income (loss)	0
Balance at the end of the period	(103,109)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at the beginning of the period	(346,359)
Current-period comprehensive income (loss)	58,257
Balance at the end of the period	$ (288,102)