PROPERTY, PLANT AND EQUIPMENT, NET - Summary (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Assets under finance leases	$ 486,563	$ 461,323
Accumulated depreciation	(291,966)	(265,586)
Accumulated depreciation of finance leases	(30)	(143)
Property and equipment, net excluding work in progress	194,567	195,594
Construction in progress	19,946	26,048
Total property, plant and equipment, net	214,513	221,642
Depreciation expense	27,900	27,100	$ 23,400
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	5,030	6,268
Land | Assets Held under Finance Leases
Property, Plant and Equipment [Line Items]
Assets under finance leases	240	225
Buildings and improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 108,370	107,721
Buildings and improvements | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment useful life	10 years
Buildings and improvements | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment useful life	35 years
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 337,792	308,457
Machinery and equipment | Assets Held under Finance Leases
Property, Plant and Equipment [Line Items]
Assets under finance leases	$ 0	200
Machinery and equipment | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment useful life	5 years
Machinery and equipment | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment useful life	25 years
Office equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 33,574	36,905
Office equipment | Assets Held under Finance Leases
Property, Plant and Equipment [Line Items]
Assets under finance leases	$ 0	31
Property, plant and equipment useful life	5 years
Office equipment | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment useful life	2 years
Office equipment | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment useful life	8 years
Vehicles
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 1,557	$ 1,516
Vehicles | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment useful life	3 years
Vehicles | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment useful life	6 years