Note 3 - Cash, Cash Equivalents, Investments and Restricted Cash - Unrealized Gains and Losses on Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Adjusted Cost	$ 250,800	$ 230,585
Available-for-sale Securities, Total	248,953	229,221
Unrealized Gains	9	17
Unrealized Losses	(1,856)	(1,381)
Fair Value of Investments in Unrealized Loss Position	197,952	215,844
Money Market Funds [Member]
Adjusted Cost	41,135	7,134
Available-for-sale Securities, Total	41,135	7,134
Corporate Debt Securities [Member]
Adjusted Cost	172,288	204,789
Available-for-sale Securities, Total	170,909	203,807
Unrealized Gains	7	17
Unrealized Losses	(1,386)	(999)
Fair Value of Investments in Unrealized Loss Position	166,204	197,564
US Government Agencies Short-term Debt Securities [Member]
Adjusted Cost	32,207	13,092
Available-for-sale Securities, Total	32,068	13,024
Unrealized Gains	2
Unrealized Losses	(141)	(68)
Fair Value of Investments in Unrealized Loss Position	28,507	13,024
Certificates of Deposit [Member]
Adjusted Cost	1,600
Available-for-sale Securities, Total	1,600
Auction Rate Securities [Member]
Adjusted Cost	3,570	5,570
Available-for-sale Securities, Total	3,241	5,256
Unrealized Losses	(329)	(314)
Fair Value of Investments in Unrealized Loss Position	$ 3,241	$ 5,256

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

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- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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- Definition

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

+ References

No definition available.

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- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

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- Definition

This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities.

+ References

No definition available.

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