Segment Information (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013 segment	Dec. 31, 2012	Dec. 31, 2011
Segment Information
Number of reportable segments									3
Segment Information
Net Sales	$ 133,092,000	$ 139,375,000	$ 140,432,000	$ 135,040,000	$ 141,777,000	$ 135,467,000	$ 148,403,000	$ 136,608,000	$ 547,939,000	$ 562,255,000	$ 541,472,000
Income (loss) from operations									68,889,000	39,861,000	57,232,000
Amortization									(2,140,000)	(1,968,000)	(1,757,000)
Restructuring charges (Note 2)					(2,200,000)	(8,000,000)			129,000	(10,211,000)
Interest income									136,000	35,000	467,000
Interest expense									(462,000)	(80,000)
Other expense - net									(1,364,000)	(2,480,000)	(1,309,000)
Income before income tax provision									67,199,000	37,336,000	56,390,000
Depreciation									26,798,000	24,352,000	22,580,000
Consolidated depreciation and amortization									28,938,000	26,320,000	24,337,000
Total assets	590,078,000				577,769,000				590,078,000	577,769,000	552,990,000
Expenditures for Long-Lived Assets									29,557,000	57,226,000	70,388,000
Accounts payable and accrued liabilities
Segment Information
Property, plant and equipment expenditures									500,000	1,500,000	2,200,000
Activated Carbon and Service
Segment Information
Net Sales									482,278,000	485,755,000	486,468,000
Depreciation									24,882,000	22,578,000	20,959,000
Total assets	527,430,000				510,550,000				527,430,000	510,550,000	493,793,000
Expenditures for Long-Lived Assets									25,885,000	56,291,000	68,533,000
Equipment
Segment Information
Net Sales									54,935,000	66,050,000	46,274,000
Depreciation									1,486,000	1,352,000	1,332,000
Total assets	55,558,000				60,191,000				55,558,000	60,191,000	53,216,000
Expenditures for Long-Lived Assets									3,325,000	550,000	752,000
Consumer
Segment Information
Net Sales									10,726,000	10,450,000	8,730,000
Depreciation									430,000	422,000	289,000
Total assets	7,090,000				7,028,000				7,090,000	7,028,000	5,981,000
Expenditures for Long-Lived Assets									347,000	385,000	1,103,000
Business operating segments
Segment Information
Income (loss) from operations									70,900,000	52,040,000	58,989,000
Business operating segments | Activated Carbon and Service
Segment Information
Income (loss) from operations									71,530,000	49,328,000	65,030,000
Business operating segments | Equipment
Segment Information
Income (loss) from operations									(2,620,000)	702,000	(3,504,000)
Business operating segments | Consumer
Segment Information
Income (loss) from operations									$ 1,990,000	$ 2,010,000	$ (2,537,000)