Income taxes - Schedule of Tax Effects of Significant Temporary Differences Comprising Deferred Tax Assets and Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Components Of Income Tax Expense Benefit [Line Items]
Intangible assets and goodwill	$ 5,471	$ 5,503
Inventories and related reserves	9,259	11,650
Accrued compensation	3,603	4,428
Allowance for doubtful accounts	7,302	4,025
Accrued interest	18,230	16,123
Net operating loss carryforwards	26,827	20,396
Other, net	987	846
Total	71,679	62,971
Valuation allowance	(26,125)	(19,115)
Deferred tax asset	45,554	43,856
Withholding taxes	(11,456)	(9,778)
Property, plant and equipment	(8,691)	(8,923)
Deferred tax liability	(20,147)	(18,701)
Net deferred tax assets	$ 25,407	$ 25,155