ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated other comprehensive income activity
Balance at the beginning of the period	$ 1,173,950
Balance at the end of the period	1,311,738	$ 1,173,950
Foreign Currency
Accumulated other comprehensive income activity
Balance at the beginning of the period	(259,888)	(206,725)	$ (42,851)
Other comprehensive income (loss) before reclassifications	74,385	(52,795)	(163,874)
Amounts reclassified from accumulated other comprehensive income		(368)
Net current-period other comprehensive income (loss)	74,385	(53,163)	(163,874)
Balance at the end of the period	(185,503)	(259,888)	(206,725)
Defined Benefit Pension Plans
Accumulated other comprehensive income activity
Balance at the beginning of the period	(59,775)	(55,550)	(67,097)
Other comprehensive income (loss) before reclassifications	(8,944)	(7,617)	6,715
Amounts reclassified from accumulated other comprehensive income	4,124	3,392	4,832
Net current-period other comprehensive income (loss)	(4,820)	(4,225)	11,547
Balance at the end of the period	(64,595)	(59,775)	(55,550)
Derivatives
Accumulated other comprehensive income activity
Balance at the beginning of the period	(46)	(72)	(97)
Other comprehensive income (loss) before reclassifications	(11,806)
Amounts reclassified from accumulated other comprehensive income	8,648	26	25
Net current-period other comprehensive income (loss)	(3,158)	26	25
Balance at the end of the period	(3,204)	(46)	(72)
Accumulated Other Comprehensive Income/(Loss)
Accumulated other comprehensive income activity
Balance at the beginning of the period	(319,709)	(262,347)	(110,045)
Other comprehensive income (loss) before reclassifications	53,635	(60,412)	(157,159)
Amounts reclassified from accumulated other comprehensive income	12,772	3,050	4,857
Net current-period other comprehensive income (loss)	66,407	(57,362)	(152,302)
Balance at the end of the period	$ (253,302)	$ (319,709)	$ (262,347)