ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Equity, beginning balance	$ 849,949
Other comprehensive income/(loss)	(10,630)	$ (37,006)
Equity, ending balance	863,686
Income tax expense related to items of other comprehensive income/(loss)	232	185
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	(11,400)	(37,700)
Amounts reclassified from accumulated other comprehensive income/(loss) (1)	0	0
Other comprehensive income/(loss)	(11,400)	(37,700)
Equity, ending balance	(163,600)	(177,900)
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)	900	700
Other comprehensive income/(loss)	900	700
Equity, ending balance	(51,700)	(49,300)
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	(11,400)	(37,700)
Amounts reclassified from accumulated other comprehensive income/(loss) (1)	900	700
Other comprehensive income/(loss)	(10,500)	(37,000)
Equity, ending balance	$ (215,300)	$ (227,200)