Fair Value Measurements and Disclosures - Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 30, 2017	Dec. 31, 2016
Assets:
Total marketable securities	$ 82,130	$ 82,899
Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	256	3,458
Total marketable securities	82,130	82,899
Total	82,386	86,357
Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	256	959
Total marketable securities	0	0
Total	256	959
Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	0	2,499
Total marketable securities	82,130	82,899
Total	82,130	85,398
Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	0	0
Total marketable securities	0	0
Total	0	0
Money market funds [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	256	959
Money market funds [Member] | Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	256	959
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
Commercial paper and corporate debt securities [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	0	2,499
Commercial paper and corporate debt securities [Member] | Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	0	0
Commercial paper and corporate debt securities [Member] | Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	0	2,499
Commercial paper and corporate debt securities [Member] | Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	0	0
U.S. Treasury securities and U.S. Government agency debt securities [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	1,495	17,072
U.S. Treasury securities and U.S. Government agency debt securities [Member] | Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	0	0
U.S. Treasury securities and U.S. Government agency debt securities [Member] | Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	1,495	17,072
U.S. Treasury securities and 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	14,497	23,019
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	14,497	23,019
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	7,949	22,402
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	7,949	22,402
Commercial paper [Member] | Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	0	0
Municipal securities and corporate debt securities [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	47,968	14,943
Municipal securities and corporate debt securities [Member] | Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	0	0
Municipal securities and corporate debt securities [Member] | Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	47,968	14,943
Municipal securities and 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	10,221	5,463
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	10,221	5,463
Asset-backed Securities [Member] | Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	$ 0	$ 0