Fair value measurement - additional information (Detail) - USD ($)	3 Months Ended	6 Months Ended
	Jun. 28, 2015	Jun. 28, 2015	Dec. 31, 2014
Fair Value Measurements [Line Items]
Contingent consideration liability	$ 3,000,000	$ 3,000,000
Fair value measurement with unobservable inputs reconciliations liability value	27,150,000	27,150,000	$ 33,433,000
Current portion of contingent consideration	5,802,000	5,802,000	$ 11,276,000
Fair value measurement with unobservable inputs reconciliations other liabilities	21,400,000	21,400,000
Minimum
Fair Value Measurements [Line Items]
Fair value of contingent consideration liability associated with future milestone	11,000,000	11,000,000
Maximum
Fair Value Measurements [Line Items]
Fair value of contingent consideration liability associated with future milestone	$ 63,963,000	$ 63,963,000