Fair Value Measurements and Disclosures, and Financial Instruments - Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 27, 2015	Dec. 27, 2014
Assets:
Total marketable securities	$ 74,789	$ 83,962
Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	1,699	610
Total marketable securities	48,368	49,286
Total	50,067	49,896
Liabilities:
Contingent consideration payable	2,073	2,397
Fair Value, Measurements, Recurring [Member] | Money market funds [Member]
Assets:
Total cash equivalents	1,699	610
Fair Value, Measurements, Recurring [Member] | U.S. Treasury, U.S. Government and U.S. Government agency debt securities [Member]
Assets:
Total marketable securities	22,532	23,034
Fair Value, Measurements, Recurring [Member] | Commercial paper and corporate debt securities [Member]
Assets:
Total marketable securities	25,836	26,252
Fair Value, Measurements, Recurring [Member] | Cash [Member]
Assets:
Total cash equivalents	24,700	34,100
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Assets:
Total cash equivalents	1,699	610
Total marketable securities	2,500	2,497
Total	4,199	3,107
Liabilities:
Contingent consideration payable	0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Money market funds [Member]
Assets:
Total cash equivalents	1,699	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	2,500	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	45,868	46,789
Total	45,868	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	20,032	20,537
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Commercial paper and corporate debt securities [Member]
Assets:
Total marketable securities	25,836	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	2,073	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