Fair Value Measurements and Disclosures (Details) (USD $) In Thousands, unless otherwise specified	Sep. 27, 2014	Dec. 28, 2013
Assets:
Total marketable securities	$ 84,373	$ 92,862
Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	1,199	1,626
Total marketable securities	48,748	48,097
Total assets	49,947	49,723
Liabilities:
Contingent consideration payable	2,431	2,783
Fair Value, Measurements, Recurring [Member] | Money market funds [Member]
Assets:
Total cash equivalents	549	876
Fair Value, Measurements, Recurring [Member] | U.S. Treasury, U.S. Government and U.S. Government agency debt securities [Member]
Assets:
Total marketable securities	21,185	17,016
Fair Value, Measurements, Recurring [Member] | Commercial paper [Member]
Assets:
Total cash equivalents	650	750
Fair Value, Measurements, Recurring [Member] | Commercial paper, municipal securities and corporate debt securities [Member]
Assets:
Total marketable securities	27,563	31,081
Fair Value, Measurements, Recurring [Member] | Cash [Member]
Assets:
Total cash equivalents	34,400	43,100
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Assets:
Total cash equivalents	549	876
Total marketable securities	2,498	5,036
Total assets	3,047	5,912
Liabilities:
Contingent consideration payable	0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Money market funds [Member]
Assets:
Total cash equivalents	549	876
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	2,498	5,036
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Commercial paper [Member]
Assets:
Total cash equivalents	0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Commercial paper, municipal securities and corporate debt securities [Member]
Assets:
Total marketable securities	0	0
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Assets:
Total cash equivalents	650	750
Total marketable securities	46,250	43,061
Total assets	46,900	43,811
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	18,687	11,980
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Commercial paper [Member]
Assets:
Total cash equivalents	650	750
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Commercial paper, municipal securities and corporate debt securities [Member]
Assets:
Total marketable securities	27,563	31,081
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Assets:
Total cash equivalents	0	0
Total marketable securities	0	0
Total assets	0	0
Liabilities:
Contingent consideration payable	2,431	2,783
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 [Member]
Assets:
Total cash equivalents	0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Commercial paper, municipal securities and corporate debt securities [Member]
Assets:
Total marketable securities	$ 0	$ 0