Fair Value Measurements and Disclosures - Assets and Liabilities Measured at Estimated Fair Value on Recurring Basis Excluding Accrued Interest Components (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	Jun. 29, 2019	Dec. 29, 2018
Assets:
Total cash equivalents	$ 37,901	$ 2,106
Total marketable securities	50,947	40,841
Total	88,848	42,947
Level 1 [Member]
Assets:
Total cash equivalents	10,964	113
Total marketable securities	0	0
Total	10,964	113
Level 2 [Member]
Assets:
Total cash equivalents	26,937	1,993
Total marketable securities	50,947	40,841
Total	77,884	42,834
Level 3 [Member]
Assets:
Total cash equivalents	0	0
Total marketable securities	0	0
Total	0	0
Money market funds [Member]
Assets:
Total cash equivalents	10,964	113
Money market funds [Member] | Level 1 [Member]
Assets:
Total cash equivalents	10,964	113
Money market funds [Member] | Level 2 [Member]
Assets:
Total cash equivalents	0	0
Money market funds [Member] | Level 3 [Member]
Assets:
Total cash equivalents	0	0
Commercial paper [Member]
Assets:
Total cash equivalents	24,937	1,993
Total marketable securities	14,066	7,932
Commercial paper [Member] | Level 1 [Member]
Assets:
Total cash equivalents	0	0
Total marketable securities	0	0
Commercial paper [Member] | Level 2 [Member]
Assets:
Total cash equivalents	24,937	1,993
Total marketable securities	14,066	7,932
Commercial paper [Member] | Level 3 [Member]
Assets:
Total cash equivalents	0	0
Total marketable securities	0	0
Certificates of deposits [Member]
Assets:
Total cash equivalents	2,000	0
Total marketable securities	13,013	9,497
Certificates of deposits [Member] | Level 1 [Member]
Assets:
Total cash equivalents	0	0
Total marketable securities	0	0
Certificates of deposits [Member] | Level 2 [Member]
Assets:
Total cash equivalents	2,000	0
Total marketable securities	13,013	9,497
Certificates of deposits [Member] | Level 3 [Member]
Assets:
Total cash equivalents	0	0
Total marketable securities	0	0
Corporate debt securities [Member]
Assets:
Total marketable securities	15,301	15,730
Corporate debt securities [Member] | Level 1 [Member]
Assets:
Total marketable securities	0	0
Corporate debt securities [Member] | Level 2 [Member]
Assets:
Total marketable securities	15,301	15,730
Corporate debt securities [Member] | Level 3 [Member]
Assets:
Total marketable securities	0	0
Asset-backed Securities [Member]
Assets:
Total marketable securities	8,567	7,682
Asset-backed Securities [Member] | Level 1 [Member]
Assets:
Total marketable securities	0	0
Asset-backed Securities [Member] | Level 2 [Member]
Assets:
Total marketable securities	8,567	7,682
Asset-backed Securities [Member] | Level 3 [Member]
Assets:
Total marketable securities	$ 0	$ 0