Income taxes (Details) (USD $)	6 Months Ended
	Jun. 28, 2014
Income Tax Disclosure [Abstract]
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	$ 9,600,000
Deferred Tax Assets, Valuation Allowance	18,600,000
Deferred Tax Assets, Net, Noncurrent	$ 44,000