Fair Value Measurements and Disclosures - Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 24, 2016	Dec. 26, 2015
Assets:
Total marketable securities	$ 81,106	$ 44,931
Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	5,084	5,158
Total marketable securities	81,106	44,931
Total	86,190	50,089
Liabilities:
Contingent consideration payable	1,333	1,490
Money market funds [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	840	590
Commercial paper and corporate debt securities [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	4,244	4,568
U.S. Treasury securities and U.S. Government agency debt securities [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	21,256	24,565
Certificates of deposits [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	16,008	0
Commercial paper [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	23,848	1,884
Municipal securities and corporate debt securities [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	12,526	18,482
Asset-backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	7,468	0
Cash [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	32,300	33,000
Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	840	590
Total marketable securities	0	4,401
Total	840	4,991
Liabilities:
Contingent consideration payable	0	0
Level 1 [Member] | Money market funds [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	840	590
Level 1 [Member] | Commercial paper and corporate debt securities [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	0	0
Level 1 [Member] | U.S. Treasury securities and U.S. Government agency debt securities [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	0	4,401
Level 1 [Member] | Certificates of deposits [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	0	0
Level 1 [Member] | Commercial paper [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	0	0
Level 1 [Member] | Municipal securities and corporate debt securities [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	0	0
Level 1 [Member] | Asset-backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	0	0
Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	4,244	4,568
Total marketable securities	81,106	40,530
Total	85,350	45,098
Liabilities:
Contingent consideration payable	0	0
Level 2 [Member] | Money market funds [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	0	0
Level 2 [Member] | Commercial paper and corporate debt securities [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	4,244	4,568
Level 2 [Member] | U.S. Treasury securities and U.S. Government agency debt securities [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	21,256	20,164
Level 2 [Member] | Certificates of deposits [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	16,008	0
Level 2 [Member] | Commercial paper [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	23,848	1,884
Level 2 [Member] | Municipal securities and corporate debt securities [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	12,526	18,482
Level 2 [Member] | Asset-backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	7,468	0
Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	0	0
Total marketable securities	0	0
Total	0	0
Liabilities:
Contingent consideration payable	1,333	1,490
Level 3 [Member] | Money market funds [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	0	0
Level 3 [Member] | Commercial paper and corporate debt securities [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	0	0
Level 3 [Member] | U.S. Treasury securities and U.S. Government agency debt securities [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	0	0
Level 3 [Member] | Certificates of deposits [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	0	0
Level 3 [Member] | Commercial paper [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	0	0
Level 3 [Member] | Municipal securities and corporate debt securities [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	0	0
Level 3 [Member] | Asset-backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	$ 0	$ 0