Note 4 - Fair Value Measurement (Details) - Financial Assets and Liabilities, Fair Value (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Assets:
Money market funds	$ 60,078us-gaap_MoneyMarketFundsAtCarryingValue	$ 35,588us-gaap_MoneyMarketFundsAtCarryingValue
Certificates of deposit	22,778
U.S. treasuries and government agency bonds	89,674	128,126
Total	180,155us-gaap_AssetsFairValueDisclosure	173,574us-gaap_AssetsFairValueDisclosure
Liabilities:
Contingent consideration	2,507
Money Market Funds [Member] \| Fair Value, Inputs, Level 1 [Member]
Assets:
Money market funds	60,078	35,588
Money Market Funds [Member]
Assets:
Money market funds	60,078	35,588
Certificates of Deposit [Member] \| Fair Value, Inputs, Level 2 [Member]
Assets:
Certificates of deposit	22,778
Certificates of Deposit [Member]
Assets:
Certificates of deposit	22,778
US Government Agencies Short-term Debt Securities [Member] \| Fair Value, Inputs, Level 2 [Member]
Assets:
U.S. treasuries and government agency bonds	89,674	128,126
US Government Agencies Short-term Debt Securities [Member]
Assets:
U.S. treasuries and government agency bonds	89,674	128,126
Auction Rate Securities [Member] \| Fair Value, Inputs, Level 3 [Member]
Assets:
Auction-rate securities backed by student-loan notes	5,389	9,860
Auction Rate Securities [Member]
Assets:
Auction-rate securities backed by student-loan notes	5,389	9,860
Equity Funds [Member] \| Fair Value, Inputs, Level 1 [Member]
Assets:
Mutual funds under deferred compensation plan	2,236
Equity Funds [Member]
Assets:
Mutual funds under deferred compensation plan	2,236
Fair Value, Inputs, Level 1 [Member]
Assets:
Total	62,314	35,588
Fair Value, Inputs, Level 2 [Member]
Assets:
Total	112,452	128,126
Fair Value, Inputs, Level 3 [Member]
Assets:
Total	5,389	9,860
Liabilities:
Contingent consideration	$ 2,507

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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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Amount of investment in debt and equity securities categorized neither as trading securities nor held-to-maturity securities and intended be sold or mature one year or operating cycle, if longer.

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Amount of liability recognized arising from contingent consideration in a business combination.

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A savings certificate entitling the Entity (that is, bearer) to receive interest at an established maturity date, based upon a fixed interest rate. A certificate of deposit may be issued in any denomination. Certificates of deposit are generally issued by commercial banks and, therefore, insured by the FDIC (up to the prescribed limit). Certificates of deposit generally restrict holders from withdrawing funds on demand without the incurrence of penalties. Generally, only certificates of deposit with original maturities of three months or less qualify as cash equivalents. Original maturity means original maturity to the entity holding the investment. As a related example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

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Investment in short-term money-market instruments (such as commercial paper, banker's acceptances, repurchase agreements, government securities, certificates of deposit, and so forth) which are highly liquid (that is, readily convertible to known amounts of cash) and so near their maturity that they present an insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify as cash equivalents by definition. Original maturity means an original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

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Other investments not otherwise specified in the taxonomy.

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Debt (bills, notes or bonds) that are issued by the government of the United States which are 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. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

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