Property, plant and equipment (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Property, plant and equipment
Total property, plant and equipment	$ 48,559	$ 47,860
Less accumulated depreciation	(27,685)	(26,520)
Net property, plant and equipment	20,874	21,340
Land
Property, plant and equipment
Total property, plant and equipment	960	960
Land improvements
Property, plant and equipment
Total property, plant and equipment	1,768	1,768
Buildings
Property, plant and equipment
Total property, plant and equipment	12,852	12,660
Machinery and equipment
Property, plant and equipment
Total property, plant and equipment	23,337	23,253
Furniture and fixtures
Property, plant and equipment
Total property, plant and equipment	7,244	7,255
Mobile equipment and other
Property, plant and equipment
Total property, plant and equipment	1,230	1,216
Construction-in-process
Property, plant and equipment
Total property, plant and equipment	$ 1,168	$ 748