Fair Value of Financial Instruments - Summary (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 30, 2017
Financial assets and liabilities measured at fair value on a recurring basis
Total short-term investments	$ 347,416	$ 494,657
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	82,111	159,662
Total short-term investments	71,459	94,575
Total assets at fair value	153,570	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	82,111	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		53,615
Total short-term investments	71,459	94,575
Recurring | Significant Other Observable Inputs (Level 2)
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	32,265	12,684
Total short-term investments	275,957	400,082
Total assets at fair value	308,222	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	23,906	11,231
Total short-term investments	151,635	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	8,359	1,453
Total short-term investments	124,322	228,247
Recurring | Significant Unobservable Inputs (Level 3)
Financial assets and liabilities measured at fair value on a recurring basis
Other assets, net	5,642	5,681
Total assets at fair value	5,642	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	5,642	5,681
Recurring | Fair Value
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	114,376	172,346
Total short-term investments	347,416	494,657
Other assets, net	5,642	5,681
Total assets at fair value	467,434	672,684
Recurring | Fair Value | Money market funds
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	82,111	106,047
Recurring | Fair Value | Corporate debt securities
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	23,906	11,231
Total short-term investments	151,635	171,835
Recurring | Fair Value | Government debt securities
Financial assets and liabilities measured at fair value on a recurring basis
Total cash equivalents	8,359	55,068
Total short-term investments	195,781	322,822
Recurring | Fair Value | Auction rate securities
Financial assets and liabilities measured at fair value on a recurring basis
Other assets, net	$ 5,642	$ 5,681