Fair Value Measurements and Disclosures - Measured at Fair Value on Recurring Basis (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	Dec. 29, 2018	Dec. 30, 2017
Assets:
Total cash equivalents	$ 2,106	$ 256
Total marketable securities	40,841	82,130
Total	42,947	82,386
Level 1 [Member]
Assets:
Total cash equivalents	113	256
Total marketable securities	0	0
Total	113	256
Level 2 [Member]
Assets:
Total cash equivalents	1,993	0
Total marketable securities	40,841	82,130
Total	42,834	82,130
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	113	256
Money market funds [Member] | Level 1 [Member]
Assets:
Total cash equivalents	113	256
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	1,993	0
Total marketable securities	7,932	7,949
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	1,993	0
Total marketable securities	7,932	7,949
Commercial paper [Member] | Level 3 [Member]
Assets:
Total cash equivalents	0	0
Total marketable securities	0	0
U.S. Government agency debt securities [Member]
Assets:
Total marketable securities	0	1,495
U.S. Government agency debt securities [Member] | Level 1 [Member]
Assets:
Total marketable securities	0	0
U.S. Government agency debt securities [Member] | Level 2 [Member]
Assets:
Total marketable securities	0	1,495
U.S. Government agency debt securities [Member] | Level 3 [Member]
Assets:
Total marketable securities	0	0
Certificates of deposits [Member]
Assets:
Total marketable securities	9,497	14,497
Certificates of deposits [Member] | Level 1 [Member]
Assets:
Total marketable securities	0	0
Certificates of deposits [Member] | Level 2 [Member]
Assets:
Total marketable securities	9,497	14,497
Certificates of deposits [Member] | Level 3 [Member]
Assets:
Total marketable securities	0	0
Corporate debt securities [Member]
Assets:
Total marketable securities	15,730	47,968
Corporate debt securities [Member] | Level 1 [Member]
Assets:
Total marketable securities	0	0
Corporate debt securities [Member] | Level 2 [Member]
Assets:
Total marketable securities	15,730	47,968
Corporate debt securities [Member] | Level 3 [Member]
Assets:
Total marketable securities	0	0
Asset-backed Securities [Member]
Assets:
Total marketable securities	7,682	10,221
Asset-backed Securities [Member] | Level 1 [Member]
Assets:
Total marketable securities	0	0
Asset-backed Securities [Member] | Level 2 [Member]
Assets:
Total marketable securities	7,682	10,221
Asset-backed Securities [Member] | Level 3 [Member]
Assets:
Total marketable securities	$ 0	$ 0