Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 30, 2017
Financial assets and liabilities measured at fair value on a recurring basis
Total short-term investments	$ 417,867	$ 494,657
Assets and liabilities measured at fair value on recurring basis | 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	136,863	159,662
Total short-term investments	65,239	94,575
Total assets at fair value	202,102	254,237
Assets and liabilities measured at fair value on recurring basis | 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	111,866	106,047
Assets and liabilities measured at fair value on recurring basis | 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	24,997	53,615
Total short-term investments	65,239	94,575
Assets and liabilities measured at fair value on recurring basis | Significant Other Observable Inputs (Level 2)
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	9,419	12,684
Total short-term investments	352,628	400,082
Total assets at fair value	362,047	412,766
Assets and liabilities measured at fair value on recurring basis | Significant Other Observable Inputs (Level 2) | Corporate debt securities
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	9,419	11,231
Total short-term investments	133,135	171,835
Assets and liabilities measured at fair value on recurring basis | 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	219,493	228,247
Assets and liabilities measured at fair value on recurring basis | Significant Unobservable Inputs (Level 3)
Financial assets and liabilities measured at fair value on a recurring basis
Other assets, net	5,609	5,681
Total assets at fair value	5,609	5,681
Assets and liabilities measured at fair value on recurring basis | Significant Unobservable Inputs (Level 3) | Auction rate securities
Financial assets and liabilities measured at fair value on a recurring basis
Other assets, net	5,609	5,681
Assets and liabilities measured at fair value on recurring basis | Fair Value
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	146,282	172,346
Total short-term investments	417,867	494,657
Other assets, net	5,609	5,681
Total assets at fair value	569,758	672,684
Assets and liabilities measured at fair value on recurring basis | Fair Value | Money market funds
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	111,866	106,047
Assets and liabilities measured at fair value on recurring basis | Fair Value | Corporate debt securities
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	9,419	11,231
Total short-term investments	133,135	171,835
Assets and liabilities measured at fair value on recurring basis | Fair Value | Government debt securities
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	24,997	55,068
Total short-term investments	284,732	322,822
Assets and liabilities measured at fair value on recurring basis | Fair Value | Auction rate securities
Financial assets and liabilities measured at fair value on a recurring basis
Other assets, net	$ 5,609	$ 5,681