Financial instruments Fair values of derivative instruments designated as hedging instruments (Details) (USD $) In Thousands, unless otherwise specified	Mar. 29, 2015	Dec. 31, 2014
Derivatives Fair Value [Line Items]
Total asset derivatives	$ 1,737	$ 0
Total liability derivatives	1,553	0
Foreign Currency Forward Contract \| Prepaid Expenses and Other Current Assets
Derivatives Fair Value [Line Items]
Total asset derivatives	1,737	0
Foreign Currency Forward Contract \| Other Current Liabilities
Derivatives Fair Value [Line Items]
Total liability derivatives	$ 1,553	$ 0

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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