Fair value measurement Valuation technique and inputs used to determine fair value of assets or liabilities (Details)	9 Months Ended
	Sep. 28, 2014
Discount Rate
Fair Value Assets And Liabilities Measured On Unobservable Inputs [Line Items]
Contingent consideration, weighted average	8.60%
Discount Rate | Minimum
Fair Value Assets And Liabilities Measured On Unobservable Inputs [Line Items]
Contingent consideration	2.30%
Discount Rate | Maximum
Fair Value Assets And Liabilities Measured On Unobservable Inputs [Line Items]
Contingent consideration	10.00%
Probability Of Payment
Fair Value Assets And Liabilities Measured On Unobservable Inputs [Line Items]
Contingent consideration, weighted average	32.00%
Probability Of Payment | Minimum
Fair Value Assets And Liabilities Measured On Unobservable Inputs [Line Items]
Contingent consideration	0.00%
Probability Of Payment | Maximum
Fair Value Assets And Liabilities Measured On Unobservable Inputs [Line Items]
Contingent consideration	100.00%