Note 8 - Cash, Cash Equivalents and Investments - Unrealized Gains and Losses on Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Adjusted Cost	$ 213,750	$ 186,854
Total Fair Value	213,292	185,831
Unrealized Gains	122	65
Unrealized Losses	(580)	(1,088)
Fair Value of Investments in Unrealized Loss Position	142,021	136,567
Money Market Funds [Member]
Adjusted Cost	11,250	24,956
Total Fair Value	11,250	24,956
Corporate Debt Securities [Member]
Adjusted Cost	180,791	110,429
Total Fair Value	180,551	109,644
Unrealized Gains	122	65
Unrealized Losses	(362)	(850)
Fair Value of Investments in Unrealized Loss Position	122,780	91,938
US Government Agencies Short-term Debt Securities [Member]
Adjusted Cost	16,139	45,899
Total Fair Value	16,123	45,877
Unrealized Gains
Unrealized Losses	(16)	(22)
Fair Value of Investments in Unrealized Loss Position	13,873	39,275
Auction Rate Securities [Member]
Adjusted Cost	5,570	5,570
Total Fair Value	5,368	5,354
Unrealized Losses	(202)	(216)
Fair Value of Investments in Unrealized Loss Position	$ 5,368	$ 5,354

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

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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