Fair Value Measurements and Disclosures - Measured at Fair Value on Recurring Basis (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	Mar. 30, 2019	Dec. 29, 2018
Assets:
Total cash equivalents	$ 15,515	$ 2,106
Total marketable securities	52,851	40,841
Total	68,366	42,947
Level 1 [Member]
Assets:
Total cash equivalents	10,526	113
Total marketable securities	0	0
Total	10,526	113
Level 2 [Member]
Assets:
Total cash equivalents	4,989	1,993
Total marketable securities	52,851	40,841
Total	57,840	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	10,526	113
Money market funds [Member] | Level 1 [Member]
Assets:
Total cash equivalents	10,526	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	3,989	1,993
Total marketable securities	16,905	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	3,989	1,993
Total marketable securities	16,905	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	11,257	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	11,257	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	16,256	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	16,256	15,730
Corporate debt securities [Member] | Level 3 [Member]
Assets:
Total marketable securities	0	0
Asset-backed Securities [Member]
Assets:
Total marketable securities	8,433	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	8,433	7,682
Asset-backed Securities [Member] | Level 3 [Member]
Assets:
Total marketable securities	$ 0	$ 0