Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) - USD ($) $ in Thousands	Apr. 01, 2018	Dec. 31, 2017
Assets:
Money market instruments	$ 7,958	$ 8,631
Financial assets at fair value	693,810
Corporate bonds
Assets:
Financial assets at fair value	380,621
Treasury bills
Assets:
Financial assets at fair value	142,299
Asset-backed securities
Assets:
Financial assets at fair value	131,678
Sovereign bonds
Assets:
Financial assets at fair value	22,780
Municipal bonds
Assets:
Financial assets at fair value	10,501
Agency bonds
Assets:
Financial assets at fair value	5,931
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Money market instruments	7,958
Cash flow hedge forward contracts	0
Economic hedge forward contracts	0
Liabilities:
Cash flow hedge forward contracts	0
Economic hedge forward contracts	0
Contingent consideration liabilities	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate bonds
Assets:
Financial assets at fair value	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Treasury bills
Assets:
Financial assets at fair value	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Asset-backed securities
Assets:
Financial assets at fair value	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Sovereign bonds
Assets:
Financial assets at fair value	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Municipal bonds
Assets:
Financial assets at fair value	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Agency bonds
Assets:
Financial assets at fair value	0
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Money market instruments	0
Cash flow hedge forward contracts	0
Economic hedge forward contracts	4
Liabilities:
Cash flow hedge forward contracts	0
Economic hedge forward contracts	18
Contingent consideration liabilities	0
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Corporate bonds
Assets:
Financial assets at fair value	380,621
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Treasury bills
Assets:
Financial assets at fair value	142,299
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Asset-backed securities
Assets:
Financial assets at fair value	131,678
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Sovereign bonds
Assets:
Financial assets at fair value	22,780
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Municipal bonds
Assets:
Financial assets at fair value	10,501
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Agency bonds
Assets:
Financial assets at fair value	5,931
Fair Value, Measurements, Recurring | Unobservable Inputs (Level 3)
Assets:
Money market instruments	0
Cash flow hedge forward contracts	0
Economic hedge forward contracts	0
Liabilities:
Cash flow hedge forward contracts	0
Economic hedge forward contracts	0
Contingent consideration liabilities	3,115
Fair Value, Measurements, Recurring | Unobservable Inputs (Level 3) | Corporate bonds
Assets:
Financial assets at fair value	0
Fair Value, Measurements, Recurring | Unobservable Inputs (Level 3) | Treasury bills
Assets:
Financial assets at fair value	0
Fair Value, Measurements, Recurring | Unobservable Inputs (Level 3) | Asset-backed securities
Assets:
Financial assets at fair value	0
Fair Value, Measurements, Recurring | Unobservable Inputs (Level 3) | Sovereign bonds
Assets:
Financial assets at fair value	0
Fair Value, Measurements, Recurring | Unobservable Inputs (Level 3) | Municipal bonds
Assets:
Financial assets at fair value	0
Fair Value, Measurements, Recurring | Unobservable Inputs (Level 3) | Agency bonds
Assets:
Financial assets at fair value	$ 0