Income taxes (Detail) (USD $)	3 Months Ended
Mar. 30, 2013	Dec. 31, 2012
Valuation Allowance, Deferred Tax Asset, Change in Amount	$ 973,000
Valuation Allowance, Amount	4,500,000
Deferred Tax Assets, Net of Valuation Allowance, Current	$ 846,000	$ 962,000

Amount after allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards expected to be realized or consumed within one year or operating cycle, if longer.

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The amount of the valuation allowance recorded as of the balance sheet date pertaining to the specified deferred tax asset for which an assessment was made that it is more likely than not that all or a portion of such deferred tax asset will not be realized through related deductions on future tax returns.

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- Definition

The amount of the change in the period in the valuation allowance for a specified deferred tax asset.

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