Schedule of Reported Financial Assets and Liabilities (Detail) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Jul. 01, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets	$ 1,304,117	$ 1,904,137
Liabilities	61,167	45,548
Other Current Liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Liabilities	253	446
Cash and Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets	480,384	429,843
Marketable securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets	712,309	1,347,979
Long-term marketable securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets	111,417	125,926
Prepayments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets	7	389
Contingent Consideration
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Liabilities	35,911	24,497
Long Term Contingent Consideration
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Liabilities	25,003	20,605
Quoted Prices in Active Markets for Identical Instruments (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets	483,451	427,720
Quoted Prices in Active Markets for Identical Instruments (Level 1) | Cash and Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets	457,352	404,290
Quoted Prices in Active Markets for Identical Instruments (Level 1) | Long-term marketable securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets	26,099	23,430
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets	820,666	1,476,417
Liabilities	253	446
Significant Other Observable Inputs (Level 2) | Other Current Liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Liabilities	253	446
Significant Other Observable Inputs (Level 2) | Cash and Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets	23,032	25,553
Significant Other Observable Inputs (Level 2) | Marketable securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets	712,309	1,347,979
Significant Other Observable Inputs (Level 2) | Long-term marketable securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets	85,318	102,496
Significant Other Observable Inputs (Level 2) | Prepayments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets	7	389
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Liabilities	60,914	45,102
Significant Unobservable Inputs (Level 3) | Contingent Consideration
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Liabilities	35,911	24,497
Significant Unobservable Inputs (Level 3) | Long Term Contingent Consideration
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Liabilities	$ 25,003	$ 20,605