Property, Plant and Equipment (Tables)

12 Months Ended

Dec. 31, 2017

Property, Plant and Equipment [Abstract]

Schedule of property, plant and equipment

For financial reporting purposes, provisions for depreciation are calculated on a straight‑line basis over the following estimated useful lives of the underlying assets:

	Years
Buildings and improvements	30-40
Machinery and equipment	5-15
Office equipment	3-10

	As of December 31,
(Dollars in thousands)	2017			2016
Land	$	14,620		$	15,855
Buildings and improvements	135,191			138,493
Machinery and equipment	238,000			220,238
Office equipment	56,554			54,013
	444,365			428,599
Accumulated depreciation	(289,909		)	(259,178		)
Property, plant and equipment, net	154,456			169,421
Equipment in process	25,155			7,495
Total property, plant and equipment, net	$	179,611		$	176,916