PROPERTY, PLANT AND EQUIPMENT - (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Total	$ 459,450		$ 457,045
Accumulated depreciation and amortization	(292,926)		(286,736)
Property, plant and equipment, net	166,524		170,309
Assets under finance leases	4,700		4,800
Accumulated amortization for assets under finance leases	1,000		900
Depreciation expense	7,500	$ 8,100
Land
Property, Plant and Equipment [Line Items]
Total	5,784		5,805
Buildings and leasehold improvements
Property, Plant and Equipment [Line Items]
Total	57,668		57,632
Machinery and equipment
Property, Plant and Equipment [Line Items]
Total	304,073		302,886
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Total	11,753		11,450
Capitalized ERP system development costs
Property, Plant and Equipment [Line Items]
Total	45,917		45,917
Computers and computer software
Property, Plant and Equipment [Line Items]
Total	20,512		20,508
Automobiles
Property, Plant and Equipment [Line Items]
Total	4,367		4,518
Construction in progress
Property, Plant and Equipment [Line Items]
Total	$ 9,376		$ 8,329