Balance Sheet Components - Marketable Securities (Details) - USD ($) $ in Thousands	Dec. 26, 2020	Dec. 28, 2019
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	$ 67,493	$ 76,231
Gross Unrealized Gains	319	123
Gross Unrealized Losses	(2)	(27)
Fair Value	67,810	76,327
Amortized Cost
Due in one year or less	50,500	38,899
Due after one year to five years	16,993	37,332
Amortized Cost	67,493	76,231
Fair Value
Due in one year or less	50,679	38,944
Due after one year to five years	17,131	37,383
Fair Value	67,810	76,327
U.S. Treasuries
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	40,602	10,458
Gross Unrealized Gains	124	11
Gross Unrealized Losses	0	0
Fair Value	40,726	10,469
Amortized Cost
Amortized Cost	40,602	10,458
Fair Value
Fair Value	40,726	10,469
Commercial paper
Debt Securities, Available-for-sale [Abstract]
Amortized Cost		3,914
Gross Unrealized Gains		1
Gross Unrealized Losses		(4)
Fair Value		3,911
Amortized Cost
Amortized Cost		3,914
Fair Value
Fair Value		3,911
Corporate bonds
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	24,156	33,867
Gross Unrealized Gains	176	68
Gross Unrealized Losses	(2)	(7)
Fair Value	24,330	33,928
Amortized Cost
Amortized Cost	24,156	33,867
Fair Value
Fair Value	24,330	33,928
Certificates of deposit
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	2,160	3,584
Gross Unrealized Gains	19	5
Gross Unrealized Losses	0	0
Fair Value	2,179	3,589
Amortized Cost
Amortized Cost	2,160	3,584
Fair Value
Fair Value	2,179	3,589
Agency securities
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	575	24,408
Gross Unrealized Gains	0	38
Gross Unrealized Losses	0	(16)
Fair Value	575	24,430
Amortized Cost
Amortized Cost	575	24,408
Fair Value
Fair Value	$ 575	$ 24,430

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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