Restructuring Charges: (Details) (USD $)	3 Months Ended		12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2013	Dec. 31, 2012
Restructuring Charges
Restructuring (income) charges during period			$ (100,000)	$ 10,200,000
Restructuring reserve activity
Accrual at beginning of period			3,226,000
Restructuring charges	2,200,000	8,000,000	(129,000)	10,211,000
Payments			(3,140,000)	(1,616,000)
Pension settlement				(1,369,000)
Non-cash charges			578,000	(4,000,000)
Accrual at end of period	3,226,000		535,000	3,226,000
Datong, China activated carbon manufacturing facility
Restructuring Charges
Impairment charges		3,600,000
Employee Termination Benefits
Restructuring reserve activity
Accrual at beginning of period			3,226,000
Restructuring charges			357,000	5,777,000
Payments			(3,048,000)	(1,182,000)
Pension settlement				(1,369,000)
Accrual at end of period	3,226,000		535,000	3,226,000
Asset Write-offs
Restructuring reserve activity
Restructuring charges				4,000,000
Non-cash charges				(4,000,000)
Gain on Sale
Restructuring reserve activity
Restructuring charges			(578,000)
Non-cash charges			578,000
Other Costs
Restructuring reserve activity
Restructuring charges			92,000	434,000
Payments			(92,000)	(434,000)
Employees Impacted
Restructuring reserve activity
Number of employees remaining to be paid			67
Number of positions reduced			4	120
Number of employees to whom amount paid			(67)	(53)
Number of employees remaining to be paid	67		4	67
Restructuring charges
Restructuring Charges
Termination benefits				4,400,000
Restructuring charges | Datong, China activated carbon manufacturing facility
Restructuring Charges
Pretax gain on sale			600,000
Impairment charges				3,600,000
Restructuring charges | Belgium warehouse
Restructuring Charges
Impairment charges				400,000
Restructuring charges | Gain on Sale | Datong, China activated carbon manufacturing facility
Restructuring Charges
Release of foreign currency translation adjustments			1,000,000
Charge for the write-off of goodwill			$ 400,000