Fair value measurement - additional information (Detail) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 27, 2015	Sep. 27, 2015	Dec. 31, 2014
Fair Value Measurements [Line Items]
Contingent consideration liability	$ 1,300,000	$ 4,300,000
Fair value measurement with unobservable inputs reconciliations liability value	22,199,000	22,199,000	$ 33,433,000
Current portion of contingent consideration	545,000	545,000	$ 11,276,000
Fair value measurement with unobservable inputs reconciliations other liabilities	21,700,000	21,700,000
Minimum
Fair Value Measurements [Line Items]
Fair value of contingent consideration liability associated with future milestone	7,055,000	7,055,000
Maximum
Fair Value Measurements [Line Items]
Fair value of contingent consideration liability associated with future milestone	$ 59,963,000	$ 59,963,000