Fair value measurement Valuation technique and inputs used to determine fair value of assets or liabilities (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 27, 2015	Sep. 27, 2015
Fair Value Assets And Liabilities Measured On Unobservable Inputs [Line Items]
Contingent consideration liability	$ 1.3	$ 4.3
Probability Of Payment
Fair Value Assets And Liabilities Measured On Unobservable Inputs [Line Items]
Contingent consideration, weighted average		52.10%
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 [Member]
Fair Value Assets And Liabilities Measured On Unobservable Inputs [Line Items]
Contingent consideration, weighted average		8.50%
Market Approach Valuation Technique [Member] | Minimum
Fair Value Assets And Liabilities Measured On Unobservable Inputs [Line Items]
Contingent consideration		3.10%
Market Approach Valuation Technique [Member] | Maximum
Fair Value Assets And Liabilities Measured On Unobservable Inputs [Line Items]
Contingent consideration		10.00%