Cash, Cash Equivalents, and Investments - Components of Cash, Cash Equivalents, and Investments (Detail) - USD ($) $ in Thousands	Apr. 01, 2018	Dec. 31, 2017	Apr. 02, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Cash	$ 101,614	$ 97,951
Money market instruments	7,958	8,631
Cash and cash equivalents	109,572	106,582	$ 92,428	$ 79,641
Short-term investments	337,629	297,961
Long-term investments	356,181	423,441
Total	803,382	827,984
Treasury bills
Schedule of Available-for-sale Securities [Line Items]
Short-term investments	138,695	150,371
Long-term investments	3,604	23,459
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Short-term investments	75,432	59,203
Long-term investments	56,246	71,727
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Short-term investments	108,313	47,395
Long-term investments	272,308	296,014
Agency bonds
Schedule of Available-for-sale Securities [Line Items]
Short-term investments	0	10,608
Long-term investments	5,931	14,890
Sovereign bonds
Schedule of Available-for-sale Securities [Line Items]
Short-term investments	6,036	21,579
Long-term investments	16,744	13,147
Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Short-term investments	9,153	8,805
Long-term investments	$ 1,348	$ 4,204