Fair Value Measurements and Disclosures - Measured at Fair Value on Recurring Basis (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	Sep. 29, 2018	Dec. 30, 2017
Assets:
Total marketable securities	$ 76,835	$ 82,130
Total	78,519	82,386
Level 1 [Member]
Assets:
Total marketable securities	0	0
Total	1,684	256
Level 2 [Member]
Assets:
Total marketable securities	76,835	82,130
Total	76,835	82,130
Level 3 [Member]
Assets:
Total marketable securities	0	0
Total	0	0
Money market funds [Member]
Assets:
Total cash equivalents	1,684	256
Money market funds [Member] | Level 1 [Member]
Assets:
Total cash equivalents	1,684	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
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	14,502	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	14,502	14,497
Certificates of deposits [Member] | Level 3 [Member]
Assets:
Total marketable securities	0	0
Commercial paper [Member]
Assets:
Total marketable securities	11,185	7,949
Commercial paper [Member] | Level 1 [Member]
Assets:
Total marketable securities	0	0
Commercial paper [Member] | Level 2 [Member]
Assets:
Total marketable securities	11,185	7,949
Commercial paper [Member] | Level 3 [Member]
Assets:
Total marketable securities	0	0
Corporate debt securities [Member]
Assets:
Total marketable securities	36,950	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	36,950	47,968
Corporate debt securities [Member] | Level 3 [Member]
Assets:
Total marketable securities	0	0
Asset-backed Securities [Member]
Assets:
Total marketable securities	14,198	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	14,198	10,221
Asset-backed Securities [Member] | Level 3 [Member]
Assets:
Total marketable securities	$ 0	$ 0