Note 8 - Cash, Cash Equivalents and Investments - Unrealized Gains and Losses on Investments (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Fair Value of Investments in Unrealized Loss Position	$ 164,066	$ 136,567
Adjusted Cost	221,533	186,854
Unrealized Gains	98	65
Unrealized Losses	(778)	(1,088)
Total Fair Value	220,853	185,831
Money Market Funds [Member]
Adjusted Cost	8,944	24,956
Total Fair Value	8,944	24,956
Certificates of Deposit [Member]
Adjusted Cost	7,378
Total Fair Value	7,378
Corporate Debt Securities [Member]
Fair Value of Investments in Unrealized Loss Position	142,294	91,938
Adjusted Cost	181,700	110,429
Unrealized Gains	96	65
Unrealized Losses	(527)	(850)
Total Fair Value	181,269	109,644
US Government Agencies Short-term Debt Securities [Member]
Fair Value of Investments in Unrealized Loss Position	16,424	39,275
Adjusted Cost	17,941	45,899
Unrealized Gains	2
Unrealized Losses	(29)	(22)
Total Fair Value	17,914	45,877
Auction Rate Securities [Member]
Fair Value of Investments in Unrealized Loss Position	5,348	5,354
Adjusted Cost	5,570	5,570
Unrealized Losses	(222)	(216)
Total Fair Value	$ 5,348	$ 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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