Fair Value of Financial Instruments - Summary of financial instruments (Details) - USD ($) $ in Thousands	Sep. 29, 2018	Dec. 30, 2017
Financial assets and liabilities measured at fair value on a recurring basis
Total short-term investments	$ 376,603	$ 494,657
Recurring
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	123,612	172,346
Total short-term investments	376,603	494,657
Other assets, net	5,750	5,681
Total assets at fair value	505,965	672,684
Recurring | Money market funds
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	89,262	106,047
Recurring | Corporate debt securities
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	27,150	11,231
Total short-term investments	187,516	171,835
Recurring | Government debt securities
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	7,200	55,068
Total short-term investments	189,087	322,822
Recurring | Auction rate securities
Financial assets and liabilities measured at fair value on a recurring basis
Other assets, net	5,750	5,681
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	89,262	159,662
Total short-term investments	61,967	94,575
Total assets at fair value	151,229	254,237
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Money market funds
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	89,262	106,047
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Government debt securities
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents		53,615
Total short-term investments	61,967	94,575
Recurring | Significant Other Observable Inputs (Level 2)
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	34,350	12,684
Total short-term investments	314,636	400,082
Total assets at fair value	348,986	412,766
Recurring | Significant Other Observable Inputs (Level 2) | Corporate debt securities
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	27,150	11,231
Total short-term investments	187,516	171,835
Recurring | Significant Other Observable Inputs (Level 2) | Government debt securities
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	7,200	1,453
Total short-term investments	127,120	228,247
Recurring | Significant Unobservable Inputs (Level 3)
Financial assets and liabilities measured at fair value on a recurring basis
Other assets, net	5,750	5,681
Total assets at fair value	5,750	5,681
Recurring | Significant Unobservable Inputs (Level 3) | Auction rate securities
Financial assets and liabilities measured at fair value on a recurring basis
Other assets, net	$ 5,750	$ 5,681