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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-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
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-Section 25
-Paragraph 1
-Subparagraph (b)
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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

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Note 5 - Financial Instruments Measured at Fair Value - Assets Measured at Fair Value on Recurring Basis (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 26, 2015
	$ 128,035	$ 117,022
Foreign Government Debt Securities [Member]
Short-term investments	623	650
Corporate Debt Securities [Member]
Short-term investments	24,108
US Government-sponsored Enterprises Debt Securities [Member]
Short-term investments	8,108
Certificates of Deposit [Member]
Short-term investments	751	1,002
Cash [Member]
Cash and cash equivalents	70,279	73,746
Money Market Funds [Member]
Cash and cash equivalents	24,166	41,624
Fair Value, Inputs, Level 1 [Member]
	70,279	73,746
Fair Value, Inputs, Level 1 [Member] \| Foreign Government Debt Securities [Member]
Short-term investments
Fair Value, Inputs, Level 1 [Member] \| Corporate Debt Securities [Member]
Short-term investments
Fair Value, Inputs, Level 1 [Member] \| US Government-sponsored Enterprises Debt Securities [Member]
Short-term investments
Fair Value, Inputs, Level 1 [Member] \| Certificates of Deposit [Member]
Short-term investments
Fair Value, Inputs, Level 1 [Member] \| Cash [Member]
Cash and cash equivalents	70,279	73,746
Fair Value, Inputs, Level 1 [Member] \| Money Market Funds [Member]
Cash and cash equivalents
Fair Value, Inputs, Level 2 [Member]
	57,756	43,276
Fair Value, Inputs, Level 2 [Member] \| Foreign Government Debt Securities [Member]
Short-term investments	623	650
Fair Value, Inputs, Level 2 [Member] \| Corporate Debt Securities [Member]
Short-term investments	24,108
Fair Value, Inputs, Level 2 [Member] \| US Government-sponsored Enterprises Debt Securities [Member]
Short-term investments	8,108
Fair Value, Inputs, Level 2 [Member] \| Certificates of Deposit [Member]
Short-term investments	751	1,002
Fair Value, Inputs, Level 2 [Member] \| Cash [Member]
Cash and cash equivalents
Fair Value, Inputs, Level 2 [Member] \| Money Market Funds [Member]
Cash and cash equivalents	24,166	41,624
Fair Value, Inputs, Level 3 [Member]

Fair Value, Inputs, Level 3 [Member] \| Foreign Government Debt Securities [Member]
Short-term investments
Fair Value, Inputs, Level 3 [Member] \| Corporate Debt Securities [Member]
Short-term investments
Fair Value, Inputs, Level 3 [Member] \| US Government-sponsored Enterprises Debt Securities [Member]
Short-term investments
Fair Value, Inputs, Level 3 [Member] \| Certificates of Deposit [Member]
Short-term investments
Fair Value, Inputs, Level 3 [Member] \| Cash [Member]
Cash and cash equivalents
Fair Value, Inputs, Level 3 [Member] \| Money Market Funds [Member]
Cash and cash equivalents