ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Equity, beginning balance			$ 798,669
Other comprehensive income/(loss)	$ 2,693	$ 1,870	(34,313)	$ (431)
Equity, ending balance	775,511		775,511
Income tax expense related to items of other comprehensive income/(loss)	185	141	370	282
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			(35,800)	(1,400)
Amounts reclassified from accumulated other comprehensive income/(loss) (1)			0	0
Other comprehensive income/(loss)			(35,800)	(1,400)
Equity, ending balance	(176,000)	(135,900)	(176,000)	(135,900)
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)			1,400	900
Other comprehensive income/(loss)			1,400	900
Equity, ending balance	(48,600)	(47,600)	(48,600)	(47,600)
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			(35,800)	(1,400)
Amounts reclassified from accumulated other comprehensive income/(loss) (1)			1,400	900
Other comprehensive income/(loss)			(34,400)	(500)
Equity, ending balance	$ (224,600)	$ (183,500)	$ (224,600)	$ (183,500)