Fair Value of Financial Instruments - Summary of financial instruments (Details) - USD ($) $ in Thousands	Mar. 30, 2019	Dec. 29, 2018
Financial assets and liabilities measured at fair value on a recurring basis
Total short-term investments	$ 382,710	$ 416,779
Recurring
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	140,157	103,148
Total short-term investments	382,710	416,779
Other assets, net	5,761	5,759
Total assets at fair value	528,628	525,686
Recurring | Money market funds
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	84,151	74,990
Recurring | Corporate debt securities
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	14,665	18,820
Total short-term investments	256,790	269,427
Recurring | Government debt securities
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	41,341	9,338
Total short-term investments	125,920	147,352
Recurring | Auction rate securities
Financial assets and liabilities measured at fair value on a recurring basis
Other assets, net	5,761	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	106,029	84,328
Total short-term investments	55,571	48,141
Total assets at fair value	161,600	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	84,151	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	21,878	9,338
Total short-term investments	55,571	48,141
Recurring | Significant Other Observable Inputs (Level 2)
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	34,128	18,820
Total short-term investments	327,139	368,638
Total assets at fair value	361,267	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	14,665	18,820
Total short-term investments	256,790	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 cash equivalents	19,463
Total short-term investments	70,349	99,211
Recurring | Significant Unobservable Inputs (Level 3)
Financial assets and liabilities measured at fair value on a recurring basis
Other assets, net	5,761	5,759
Total assets at fair value	5,761	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	$ 5,761	$ 5,759