Cash, Cash Equivalents, and Investments - Components of Cash, Cash Equivalents, and Investments (Detail) - USD ($) $ in Thousands	Jul. 01, 2018	Dec. 31, 2017	Jul. 02, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Cash	$ 124,147	$ 97,951
Money market instruments	5,055	8,631
Cash and cash equivalents	129,202	106,582	$ 68,266	$ 79,641
Short-term investments	353,740	297,961
Long-term investments	271,941	423,441
Total	754,883	827,984
Treasury Bills
Schedule of Available-for-sale Securities [Line Items]
Short-term investments	136,377	150,371
Long-term investments	0	23,459
Corporate Bonds
Schedule of Available-for-sale Securities [Line Items]
Short-term investments	116,347	47,395
Long-term investments	208,454	296,014
Asset-Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Short-term investments	55,240	59,203
Long-term investments	47,740	71,727
Sovereign Bonds
Schedule of Available-for-sale Securities [Line Items]
Short-term investments	7,375	21,579
Long-term investments	8,971	13,147
Agency Bonds
Schedule of Available-for-sale Securities [Line Items]
Short-term investments	29,247	10,608
Long-term investments	5,934	14,890
Municipal Bonds
Schedule of Available-for-sale Securities [Line Items]
Short-term investments	9,154	8,805
Long-term investments	$ 842	$ 4,204