Note 3 - Cash, Cash Equivalents and Investments - Unrealized Gains and Losses on Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Adjusted Cost	$ 186,854	$ 182,482
Available-for-sale Securities	185,831	182,107
Unrealized Gains	65	4
Unrealized Losses	(1,088)	(379)
Fair Value of Investments in Unrealized Loss Position	136,567	116,081
Money Market Funds [Member]
Adjusted Cost	24,956	31,640
Available-for-sale Securities	24,956	31,640
Corporate Debt Securities [Member]
Adjusted Cost	110,429
Available-for-sale Securities	109,644
Unrealized Gains	65
Unrealized Losses	(850)
Fair Value of Investments in Unrealized Loss Position	91,938
Certificates of Deposit [Member]
Adjusted Cost		21,574
Available-for-sale Securities		21,574
US Government Agencies Short-term Debt Securities [Member]
Adjusted Cost	45,899	123,698
Available-for-sale Securities	45,877	123,532
Unrealized Gains		4
Unrealized Losses	(22)	(170)
Fair Value of Investments in Unrealized Loss Position	39,275	110,720
Auction Rate Securities [Member]
Adjusted Cost	5,570	5,570
Available-for-sale Securities	5,354	5,361
Unrealized Losses	(216)	(209)
Fair Value of Investments in Unrealized Loss Position	$ 5,354	$ 5,361

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

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