Assets - Property, Plant, and Equipment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Property, plant, and equipment
Gross property, plant and equipment	$ 200,144		$ 200,144		$ 197,020
Less: accumulated depreciation and amortization	119,518		119,518		111,962
Net property, plant, and equipment	80,626		80,626		85,058
Depreciation expense	4,600	$ 4,200	13,000	$ 10,600
Land
Property, plant, and equipment
Gross property, plant and equipment	5,669		5,669		5,669
Building and improvements
Property, plant, and equipment
Gross property, plant and equipment	59,547		59,547		54,449
Machinery and equipment
Property, plant, and equipment
Gross property, plant and equipment	126,126		126,126		126,829
Leaseholds improvements
Property, plant, and equipment
Gross property, plant and equipment	$ 8,802		$ 8,802		$ 10,073