Fair value measurement Financial assets and liabilities carried at fair value measured on recurring basis (Details) - USD ($) $ in Thousands	Sep. 27, 2015	Dec. 31, 2014
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments in marketable securities	$ 6,560	$ 6,863
Derivative assets	914
Derivative liabilities	3,510
Contingent consideration liabilities	22,199	33,433
Quoted prices in active markets (Level 1)
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments in marketable securities	6,560	6,863
Derivative assets	0
Derivative liabilities	0
Contingent consideration liabilities	0	0
Significant other observable Inputs (Level 2)
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments in marketable securities	0	0
Derivative assets	914
Derivative liabilities	3,510
Contingent consideration liabilities	0	0
Significant unobservable Inputs (Level 3)
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments in marketable securities	0	0
Derivative assets	0
Derivative liabilities	0
Contingent consideration liabilities	$ 22,199	$ 33,433