Fair Value of Financial Instruments - Summary of financial instruments (Details) - USD ($) $ in Thousands	Dec. 29, 2018	Dec. 30, 2017
Financial assets and liabilities measured at fair value on a recurring basis
Total short-term investments	$ 416,779	$ 494,657
Recurring
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	103,148	172,346
Total short-term investments	416,779	494,657
Other assets, net	5,759	5,681
Total assets at fair value	525,686	672,684
Recurring | Money market funds
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	74,990	106,047
Recurring | Corporate debt securities
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	18,820	11,231
Total short-term investments	269,427	171,835
Recurring | Government debt securities
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	9,338	55,068
Total short-term investments	147,352	322,822
Recurring | Auction rate securities
Financial assets and liabilities measured at fair value on a recurring basis
Other assets, net	5,759	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	84,328	159,662
Total short-term investments	48,141	94,575
Total assets at fair value	132,469	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	74,990	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	9,338	53,615
Total short-term investments	48,141	94,575
Recurring | Significant Other Observable Inputs (Level 2)
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	18,820	12,684
Total short-term investments	368,638	400,082
Total assets at fair value	387,458	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	18,820	11,231
Total short-term investments	269,427	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		1,453
Total short-term investments	99,211	228,247
Recurring | Significant Unobservable Inputs (Level 3)
Financial assets and liabilities measured at fair value on a recurring basis
Other assets, net	5,759	5,681
Total assets at fair value	5,759	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	$ 5,759	$ 5,681