ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Equity, beginning balance	$ 702,621
Other comprehensive income	7,596	$ 8,894
Equity, ending balance	722,556
Tax (benefit)/expense	177	252
Foreign Currency Translation Adjustments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Equity, beginning balance	(99,700)	(118,400)
Other comprehensive income/(loss) before reclassifications	6,900	8,400
Amounts reclassified from accumulated other comprehensive income/(loss) (1)	0	0
Other comprehensive income	6,900	8,400
Equity, ending balance	(92,800)	(110,000)
Pension and Post-Retirement Plan Benefit Adjustments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Equity, beginning balance	(49,300)	(51,500)
Other comprehensive income/(loss) before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive income/(loss) (1)	600	500
Other comprehensive income	600	500
Equity, ending balance	(48,700)	(51,000)
AOCI Including Portion Attributable to Noncontrolling Interest
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Equity, beginning balance	(149,000)	(169,900)
Other comprehensive income/(loss) before reclassifications	6,900	8,400
Amounts reclassified from accumulated other comprehensive income/(loss) (1)	600	500
Other comprehensive income	7,500	8,900
Equity, ending balance	$ (141,500)	$ (161,000)