ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Equity, beginning balance			$ 702,621
Other comprehensive income	$ (10,140)	$ 6,920	(34,682)	$ 22,410
Equity, ending balance	736,345		736,345
Income tax expense related to items of other comprehensive income	176	281	529	785
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			(36,600)	21,600
Amounts reclassified from accumulated other comprehensive income/(loss) (1)			0	0
Other comprehensive income			(36,600)	21,600
Equity, ending balance	(136,300)	(96,800)	(136,300)	(96,800)
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)			1,800	1,500
Other comprehensive income			1,800	1,500
Equity, ending balance	(47,500)	(50,000)	(47,500)	(50,000)
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			(36,600)	21,600
Amounts reclassified from accumulated other comprehensive income/(loss) (1)			1,800	1,500
Other comprehensive income			(34,800)	23,100
Equity, ending balance	$ (183,800)	$ (146,800)	$ (183,800)	$ (146,800)