Fair value measurement Valuation technique and inputs used to determine fair value of assets or liabilities (Details)	3 Months Ended
	Mar. 27, 2016
Probability Of Payment
Fair Value Assets And Liabilities Measured On Unobservable Inputs [Line Items]
Contingent consideration, weighted average	52.70%
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%
Market Approach Valuation Technique
Fair Value Assets And Liabilities Measured On Unobservable Inputs [Line Items]
Contingent consideration, weighted average	8.30%
Market Approach Valuation Technique | Minimum
Fair Value Assets And Liabilities Measured On Unobservable Inputs [Line Items]
Contingent consideration	2.60%
Market Approach Valuation Technique | Maximum
Fair Value Assets And Liabilities Measured On Unobservable Inputs [Line Items]
Contingent consideration	10.00%