Segment Information - Results of Operations (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2015 USD ($) segment	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Segment Information
Number of reportable segments | segment									3
Net Sales	$ 130,873	$ 132,976	$ 135,452	$ 135,703	$ 140,640	$ 137,699	$ 145,132	$ 131,632	$ 535,004	$ 555,103	$ 547,939
Income from operations									64,794	74,605	68,889
Restructuring income										252	129
Interest income									58	77	136
Interest expense									(773)	(263)	(462)
Other income (expense) - net									(693)	(1,911)	(1,364)
Income before income tax provision									63,386	72,508	67,199
Depreciation and amortization									35,453	30,470	28,938
Activated Carbon and Service
Segment Information
Net Sales									486,548	498,212	482,278
Depreciation and amortization									32,443	26,820	25,395
Equipment
Segment Information
Net Sales									39,293	45,319	54,935
Depreciation and amortization									2,400	3,049	2,907
Consumer
Segment Information
Net Sales									9,163	11,572	10,726
Depreciation and amortization									610	601	636
Business operating segments
Segment Information
Income from operations									64,794	74,353	68,760
Business operating segments | Activated Carbon and Service
Segment Information
Income from operations									67,583	78,114	71,017
Business operating segments | Equipment
Segment Information
Income from operations									(4,210)	(5,657)	(4,041)
Business operating segments | Consumer
Segment Information
Income from operations									$ 1,421	$ 1,896	$ 1,784