EMPLOYEE BENEFIT PLANS - Amounts Recognized in Statement of Financial Position and Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Amounts recognized in the statement of financial position
Noncurrent assets/(liabilities)	$ 17,595	$ (2,880)
Amounts recognized in accumulated other comprehensive income
Net actuarial loss	61,598	80,662
Changes in pension liability (charged) credited to other comprehensive income (loss)	$ 19,000	$ 3,000	$ 14,800