Fair value measurement - Additional Information (Detail) - USD ($) $ in Thousands	Sep. 25, 2016	Dec. 31, 2015
Fair Value Measurements [Line Items]
Fair value measurement with unobservable inputs reconciliations liability value	$ 22,368	$ 20,829
Current portion of contingent consideration	7,539	$ 7,291
Fair value measurement with unobservable inputs reconciliations other liabilities	14,900
Minimum
Fair Value Measurements [Line Items]
Fair value of contingent consideration liability associated with future milestone	7,000
Maximum
Fair Value Measurements [Line Items]
Fair value of contingent consideration liability associated with future milestone	$ 46,300