Fair Value of Financial Instruments - Summary of financial instruments (Details) - USD ($) $ in Thousands	Jun. 29, 2019	Dec. 29, 2018
Financial assets and liabilities measured at fair value on a recurring basis
Total short-term investments	$ 452,265	$ 416,779
Recurring
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	96,093	103,148
Total short-term investments	452,265	416,779
Other assets, net	5,647	5,759
Total assets at fair value	554,005	525,686
Recurring | Money market funds
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	84,467	74,990
Recurring | Corporate debt securities
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	11,626	18,820
Total short-term investments	285,944	269,427
Recurring | Government debt securities
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents		9,338
Total short-term investments	166,321	147,352
Recurring | Auction rate securities
Financial assets and liabilities measured at fair value on a recurring basis
Other assets, net	5,647	5,759
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	84,467	84,328
Total short-term investments	72,422	48,141
Total assets at fair value	156,889	132,469
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	84,467	74,990
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		9,338
Total short-term investments	72,422	48,141
Recurring | Significant Other Observable Inputs (Level 2)
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	11,626	18,820
Total short-term investments	379,843	368,638
Total assets at fair value	391,469	387,458
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	11,626	18,820
Total short-term investments	285,944	269,427
Recurring | Significant Other Observable Inputs (Level 2) | Government debt securities
Financial assets and liabilities measured at fair value on a recurring basis
Total short-term investments	93,899	99,211
Recurring | Significant Unobservable Inputs (Level 3)
Financial assets and liabilities measured at fair value on a recurring basis
Other assets, net	5,647	5,759
Total assets at fair value	5,647	5,759
Recurring | Significant Unobservable Inputs (Level 3) | Auction rate securities
Financial assets and liabilities measured at fair value on a recurring basis
Other assets, net	$ 5,647	$ 5,759