ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Equity, beginning balance			$ 849,949
Other comprehensive income/(loss)	$ (11,170)	$ 4,138	(12,780)	$ (30,175)
Equity, ending balance	925,724		925,724
Income tax expense related to items of other comprehensive income/(loss)	243	192	707	562
Foreign Currency Translation Adjustments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Equity, beginning balance			(152,200)	(140,200)
Other comprehensive income/(loss) before reclassifications			(15,300)	(32,400)
Amounts reclassified from accumulated other comprehensive income/(loss) (1)			0	0
Other comprehensive income/(loss)			(15,300)	(32,400)
Equity, ending balance	(167,500)	(172,600)	(167,500)	(172,600)
Pension and Post-Retirement Plan Benefit Adjustments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Equity, beginning balance			(52,600)	(50,000)
Other comprehensive income/(loss) before reclassifications			0	0
Amounts reclassified from accumulated other comprehensive income/(loss) (1)			2,700	2,200
Other comprehensive income/(loss)			2,700	2,200
Equity, ending balance	(49,900)	(47,800)	(49,900)	(47,800)
AOCI Including Portion Attributable to Noncontrolling Interest
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Equity, beginning balance			(204,800)	(190,200)
Other comprehensive income/(loss) before reclassifications			(15,300)	(32,400)
Amounts reclassified from accumulated other comprehensive income/(loss) (1)			2,700	2,200
Other comprehensive income/(loss)			(12,600)	(30,200)
Equity, ending balance	$ (217,400)	$ (220,400)	$ (217,400)	$ (220,400)