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
Income Tax Disclosure [Abstract]
Intangible assets and goodwill	$ 5,346	$ 5,300
Inventories and related reserves	14,020	13,756
Deferred revenue and cost of sales	11,682	7,631
Other accruals and reserves	3,868	10,287
Accrued compensation	3,817	4,444
Allowance for doubtful accounts	3,718	4,029
Accrued interest	18,229	16,123
Net operating loss carryforwards	27,231	20,849
Other, net	539	(349)
Total	88,450	82,070
Valuation allowance	(26,361)	(19,124)
Deferred tax asset	62,089	62,946
Withholding taxes	(11,456)	(9,778)
Property, plant and equipment	(9,758)	(9,892)
Deferred tax liability	(21,214)	(19,670)
Net deferred tax assets	$ 40,875	$ 43,276