Commitments and contingent liabilities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified			9 Months Ended							9 Months Ended
	Sep. 28, 2014	Dec. 31, 2013	Sep. 28, 2014 Minimum	Sep. 28, 2014 Maximum	Sep. 28, 2014 Accrued Liabilities	Dec. 31, 2013 Accrued Liabilities	Sep. 28, 2014 Other Liability	Dec. 31, 2013 Other Liability	Sep. 28, 2014 Property, Plant and Equipment	Sep. 28, 2014 Property, Plant and Equipment Build To Suit Lease
Loss Contingencies [Line Items]
Estimated fair value of the costs to construct buildings									$ 28.2	$ 28.3
Lease commencement date										Sep. 01, 2013
Waste disposed accrued liability					2.2	2.5	5.3	5.8
Time-frame over which the accrued amounts may be paid out, in years			15 years	20 years
Contingency reserve for litigation	$ 4.2	$ 6.8
Expected construction completion year										2014-10