Fair Value of Financial Instruments - Summary of financial instruments (Details) - USD ($) $ in Thousands	Dec. 28, 2019	Dec. 29, 2018
Financial assets and liabilities measured at fair value on a recurring basis
Total short-term investments	$ 498,825	$ 416,779
Recurring
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	93,704	103,148
Total short-term investments	498,825	416,779
Other assets, net	5,647	5,759
Total assets at fair value	598,176	525,686
Recurring | Money market funds
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	92,379	74,990
Recurring | Corporate debt securities
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	1,325	18,820
Total short-term investments	326,954	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	171,871	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	92,379	84,328
Total short-term investments	85,189	48,141
Total assets at fair value	177,568	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	92,379	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	85,189	48,141
Recurring | Significant Other Observable Inputs (Level 2)
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	1,325	18,820
Total short-term investments	413,636	368,638
Total assets at fair value	414,961	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	1,325	18,820
Total short-term investments	326,954	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	86,682	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