Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) - USD ($) $ in Thousands	Jul. 01, 2018	Dec. 31, 2017
Assets:
Money market instruments	$ 5,055	$ 8,631
Financial assets at fair value	625,681
Corporate Bonds
Assets:
Financial assets at fair value	324,801
Treasury Bills
Assets:
Financial assets at fair value	136,377
Asset-Backed Securities
Assets:
Financial assets at fair value	102,980
Sovereign Bonds
Assets:
Financial assets at fair value	16,346
Agency Bonds
Assets:
Financial assets at fair value	35,181
Municipal Bonds
Assets:
Financial assets at fair value	9,996
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Assets:
Money market instruments	5,055
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Assets:
Money market instruments	0
Economic hedge forward contracts	0
Liabilities:
Economic hedge forward contracts	(86)
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Corporate Bonds
Assets:
Financial assets at fair value	324,801
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Treasury Bills
Assets:
Financial assets at fair value	136,377
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Asset-Backed Securities
Assets:
Financial assets at fair value	102,980
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Sovereign Bonds
Assets:
Financial assets at fair value	16,346
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Agency Bonds
Assets:
Financial assets at fair value	35,181
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Municipal Bonds
Assets:
Financial assets at fair value	9,996
Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring
Liabilities:
Contingent consideration liabilities	$ 2,303