Property, plant and equipment (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Property, plant and equipment
Total property, plant and equipment	$ 71,988	$ 56,660
Less accumulated depreciation	(34,442)	(31,794)
Net property, plant and equipment	37,546	24,866
Land
Property, plant and equipment
Total property, plant and equipment	1,500	1,160
Land improvements
Property, plant and equipment
Total property, plant and equipment	2,292	1,849
Leasehold Improvements
Property, plant and equipment
Total property, plant and equipment	499
Buildings
Property, plant and equipment
Total property, plant and equipment	21,918	16,743
Machinery and equipment
Property, plant and equipment
Total property, plant and equipment	31,780	25,756
Furniture and fixtures
Property, plant and equipment
Total property, plant and equipment	10,070	8,772
Mobile equipment and other
Property, plant and equipment
Total property, plant and equipment	1,999	1,267
Construction-in-process
Property, plant and equipment
Total property, plant and equipment	$ 1,930	$ 1,113