Schedule of Carrying Amounts and Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands		Apr. 01, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Marketable securities		$ 927,172	$ 1,473,905
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Cash and cash equivalents		637,873	429,843
Marketable securities		949,785	1,473,905
Derivative assets		12	389
Contingent consideration		15,581	45,102
Derivative liabilities		224	446
Convertible debt	[1]	369,421	365,987
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Cash and cash equivalents		637,873	429,843
Marketable securities		949,785	1,473,905
Derivative assets		12	389
Contingent consideration		15,581	45,102
Derivative liabilities		224	446
Convertible debt	[1]	$ 700,626	$ 659,525

[1] The carrying value represents the bifurcated debt component only, while the fair value is based on quoted market prices for the convertible note which includes the equity conversion features.