ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Equity, beginning balance			$ 798,669
Other comprehensive income/(loss)	$ 4,138	$ (13,184)	(30,175)	$ (13,615)
Equity, ending balance	812,442		812,442
Income tax expense related to items of other comprehensive income/(loss)	192	131	562	413
Foreign Currency Translation Adjustments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Equity, beginning balance			(140,200)	(134,500)
Other comprehensive income/(loss) before reclassifications			(32,400)	(15,100)
Amounts reclassified from accumulated other comprehensive income/(loss) (1)			0	0
Other comprehensive income/(loss)			(32,400)	(15,100)
Equity, ending balance	(172,600)	(149,600)	(172,600)	(149,600)
Pension and Post-Retirement Plan Benefit Adjustments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Equity, beginning balance			(50,000)	(48,500)
Other comprehensive income/(loss) before reclassifications			0	0
Amounts reclassified from accumulated other comprehensive income/(loss) (1)			2,200	1,500
Other comprehensive income/(loss)			2,200	1,500
Equity, ending balance	(47,800)	(47,000)	(47,800)	(47,000)
AOCI Including Portion Attributable to Noncontrolling Interest
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Equity, beginning balance			(190,200)	(183,000)
Other comprehensive income/(loss) before reclassifications			(32,400)	(15,100)
Amounts reclassified from accumulated other comprehensive income/(loss) (1)			2,200	1,500
Other comprehensive income/(loss)			(30,200)	(13,600)
Equity, ending balance	$ (220,400)	$ (196,600)	$ (220,400)	$ (196,600)