Fair Value Measurements and Disclosures - Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 30, 2017
Assets:
Total marketable securities	$ 57,975	$ 82,130
Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	57,975	82,130
Total	67,655	82,386
Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	0	0
Total	9,680	256
Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	57,975	82,130
Total	57,975	82,130
Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	0	0
Total	0	0
Money market funds [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	9,680	256
Money market funds [Member] | Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	9,680	256
Money market funds [Member] | Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	0	0
Money market funds [Member] | Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	0	0
U.S. Government agency debt securities [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	1,496	1,495
U.S. Government agency debt securities [Member] | Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	0	0
U.S. Government agency debt securities [Member] | Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	1,496	1,495
U.S. Government agency debt securities [Member] | Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	0	0
Certificates of deposits [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	6,995	14,497
Certificates of deposits [Member] | Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	0	0
Certificates of deposits [Member] | Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	6,995	14,497
Certificates of deposits [Member] | Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	0	0
Commercial paper [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	5,474	7,949
Commercial paper [Member] | Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	0	0
Commercial paper [Member] | Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	5,474	7,949
Commercial paper [Member] | Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	0	0
Corporate debt securities [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	36,842	47,968
Corporate debt securities [Member] | Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	0	0
Corporate debt securities [Member] | Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	36,842	47,968
Corporate debt securities [Member] | Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	0	0
Asset-backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	7,168	10,221
Asset-backed Securities [Member] | Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	0	0
Asset-backed Securities [Member] | Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	7,168	10,221
Asset-backed Securities [Member] | Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	$ 0	$ 0