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	Sep. 28, 2019	Dec. 29, 2018
Assets:
Total cash equivalents	$ 16,147	$ 2,106
Total marketable securities	93,101	40,841
Total	109,248	42,947
Level 1 [Member]
Assets:
Total cash equivalents	9,162	113
Total marketable securities	0	0
Total	9,162	113
Level 2 [Member]
Assets:
Total cash equivalents	6,985	1,993
Total marketable securities	93,101	40,841
Total	100,086	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	9,162	113
Money market funds [Member] | Level 1 [Member]
Assets:
Total cash equivalents	9,162	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	5,985	1,993
Total marketable securities	16,759	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	5,985	1,993
Total marketable securities	16,759	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	1,000	0
Total marketable securities	29,007	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	1,000	0
Total marketable securities	29,007	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	36,927	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	36,927	15,730
Corporate debt securities [Member] | Level 3 [Member]
Assets:
Total marketable securities	0	0
Asset-backed Securities [Member]
Assets:
Total marketable securities	10,408	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	10,408	7,682
Asset-backed Securities [Member] | Level 3 [Member]
Assets:
Total marketable securities	$ 0	$ 0