Income taxes (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Income taxes
U.S.	$ 18,762,000	$ 57,849,000	$ 28,542,000
Non-U.S.	1,941,000	14,549,000	11,479,000
Income before income taxes	20,703,000	72,398,000	40,021,000
U.S.
Current	17,351,000	23,208,000	17,929,000
Deferred	(169,000)	(1,533,000)	(6,698,000)
Non-U.S.
Current	3,489,000	4,804,000	2,029,000
Deferred	1,105,000	1,711,000	2,289,000
Total tax expense	21,776,000	28,190,000	15,549,000
Components of deferred tax assets and liabilities
Patents, trademarks, other intangible assets and goodwill	(5,144,000)	(6,048,000)
Property, plant and equipment	(9,767,000)	(6,672,000)
Withholding taxes	(9,777,000)	(8,102,000)
Inventories and related reserves	11,920,000	11,576,000
Accrued compensation	6,833,000	15,484,000
Allowance for doubtful accounts	4,278,000	4,163,000
Interest	16,123,000	12,471,000
Net operating loss carryforwards	20,161,000	21,790,000
Other, net	1,241,000	1,856,000
Valuation allowance	(19,116,000)	(21,023,000)
Net deferred tax asset	16,752,000	25,495,000
Net decrease in valuation allowance		1,900,000
Operating loss carry forwards, state, net of tax	23,700,000
Operating loss carry forwards, foreign, net of tax	74,100,000
Reclassification for tax benefit on exercise of stock options	$ 8,999,000