Fair Value Measurements and Disclosures - Measured at Fair Value on Recurring Basis (Details) (USD $) In Thousands, unless otherwise specified	Mar. 28, 2015	Dec. 27, 2014
Assets:
Total marketable securities	$ 77,049	$ 83,962
Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	909	610
Total marketable securities	49,114	49,286
Total	50,023	49,896
Liabilities:
Contingent consideration payable	2,208	2,397
Fair Value, Measurements, Recurring [Member] | Money market funds [Member]
Assets:
Total cash equivalents	909	610
Fair Value, Measurements, Recurring [Member] | U.S. Treasury, U.S. Government and U.S. Government agency debt securities [Member]
Assets:
Total marketable securities	24,053	23,034
Fair Value, Measurements, Recurring [Member] | Commercial paper and corporate debt securities [Member]
Assets:
Total marketable securities	25,061	26,252
Fair Value, Measurements, Recurring [Member] | Cash [Member]
Assets:
Total cash equivalents	27,000	34,100
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Assets:
Total cash equivalents	909	610
Total marketable securities	2,499	2,497
Total	3,408	3,107
Liabilities:
Contingent consideration payable	0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Money market funds [Member]
Assets:
Total cash equivalents	909	610
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | U.S. Treasury, U.S. Government and U.S. Government agency debt securities [Member]
Assets:
Total marketable securities	2,499	2,497
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Commercial paper and corporate debt securities [Member]
Assets:
Total marketable securities	0	0
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Assets:
Total cash equivalents	0	0
Total marketable securities	46,615	46,789
Total	46,615	46,789
Liabilities:
Contingent consideration payable	0	0
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Money market funds [Member]
Assets:
Total cash equivalents	0	0
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | U.S. Treasury, U.S. Government and U.S. Government agency debt securities [Member]
Assets:
Total marketable securities	21,554	20,537
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Commercial paper and corporate debt securities [Member]
Assets:
Total marketable securities	25,061	26,252
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Assets:
Total cash equivalents	0	0
Total marketable securities	0	0
Total	0	0
Liabilities:
Contingent consideration payable	2,208	2,397
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Money market funds [Member]
Assets:
Total cash equivalents	0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | U.S. Treasury, U.S. Government and U.S. Government agency debt securities [Member]
Assets:
Total marketable securities	0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Commercial paper and corporate debt securities [Member]
Assets:
Total marketable securities	$ 0	$ 0