Property, plant and equipment (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Property, plant and equipment
Total property, plant and equipment	$ 82,472	$ 81,540
Less accumulated depreciation	(40,054)	(38,904)
Net property, plant and equipment	42,418	42,636
Land
Property, plant and equipment
Total property, plant and equipment	1,500	1,500
Land improvements
Property, plant and equipment
Total property, plant and equipment	3,010	3,010
Leasehold Improvements
Property, plant and equipment
Total property, plant and equipment	859	859
Buildings
Property, plant and equipment
Total property, plant and equipment	24,481	24,476
Machinery and equipment
Property, plant and equipment
Total property, plant and equipment	36,777	35,628
Furniture and fixtures
Property, plant and equipment
Total property, plant and equipment	11,663	11,657
Mobile equipment and other
Property, plant and equipment
Total property, plant and equipment	2,430	2,255
Construction-in-process
Property, plant and equipment
Total property, plant and equipment	$ 1,752	$ 2,155