Segment Information - Net Sales by Product (Details 3) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net Sales by Product
Net Sales	$ 130,873	$ 132,976	$ 135,452	$ 135,703	$ 140,640	$ 137,699	$ 145,132	$ 131,632	$ 535,004	$ 555,103	$ 547,939
Carbon products
Net Sales by Product
Net Sales									460,251	474,222	460,681
Capital equipment
Net Sales by Product
Net Sales									35,114	41,238	49,036
Equipment leasing
Net Sales by Product
Net Sales									15,235	16,598	15,127
Carbon cloth products
Net Sales by Product
Net Sales									9,163	11,564	10,721
Spare parts
Net Sales by Product
Net Sales									4,179	4,081	5,899
Other services
Net Sales by Product
Net Sales									$ 11,062	$ 7,400	$ 6,475