Fair Value Measurements and Disclosures - Measured at Fair Value on Recurring Basis (Details) (USD $) In Thousands, unless otherwise specified	Dec. 27, 2014	Dec. 28, 2013
Assets:
Total marketable securities	$ 83,962us-gaap_AvailableForSaleSecurities	$ 92,862us-gaap_AvailableForSaleSecurities
Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	610	1,626
Total marketable securities	49,286	48,097
Total	49,896	49,723
Liabilities:
Contingent consideration payable	2,397	2,783
Fair Value, Measurements, Recurring [Member] \| Money market funds [Member]
Assets:
Total cash equivalents	610	876
Fair Value, Measurements, Recurring [Member] \| U.S. Treasury, U.S. Government and U.S. Government agency debt securities [Member]
Assets:
Total marketable securities	23,034	17,016
Fair Value, Measurements, Recurring [Member] \| Commercial paper and corporate debt securities [Member]
Assets:
Total cash equivalents	0	750
Total marketable securities	26,252	31,081
Fair Value, Measurements, Recurring [Member] \| Cash [Member]
Assets:
Total cash equivalents	34,100	43,100
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member]
Assets:
Total cash equivalents	610	876
Total marketable securities	2,497	5,036
Total	3,107	5,912
Liabilities:
Contingent consideration payable	0	0
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member] \| Money market funds [Member]
Assets:
Total cash equivalents	610	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	2,497	5,036
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member] \| Commercial paper and corporate debt securities [Member]
Assets:
Total cash equivalents	0	0
Total marketable securities	0	0
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member]
Assets:
Total cash equivalents	0	750
Total marketable securities	46,789	43,061
Total	46,789	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	20,537	11,980
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| Commercial paper and corporate debt securities [Member]
Assets:
Total cash equivalents	0	750
Total marketable securities	26,252	31,081
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	2,397	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 and corporate debt securities [Member]
Assets:
Total cash equivalents	0	0
Total marketable securities	$ 0	$ 0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash

-URI http://asc.fasb.org/extlink&oid=6506951

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-Name Accounting Standards Codification

-Glossary Cash Equivalents

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Fair value of financial and nonfinancial obligations.

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