Note 9 - Cash, Cash Equivalents, Investments and Restricted Cash - Unrealized Gains and Losses on Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Adjusted Cost	$ 249,405	$ 230,585
Total Fair Value	247,246	229,221
Unrealized Gains	2	17
Unrealized Losses	(2,161)	(1,381)
Fair Value of Investments in Unrealized Loss Position	216,846	215,844
Money Market Funds [Member]
Adjusted Cost	25,235	7,134
Total Fair Value	25,235	7,134
Corporate Debt Securities [Member]
Adjusted Cost	192,581	204,789
Total Fair Value	190,924	203,807
Unrealized Gains	2	17
Unrealized Losses	(1,659)	(999)
Fair Value of Investments in Unrealized Loss Position	187,359	197,564
US Government Agencies Short-term Debt Securities [Member]
Adjusted Cost	24,419	13,092
Total Fair Value	24,230	13,024
Unrealized Losses	(189)	(68)
Fair Value of Investments in Unrealized Loss Position	24,230	13,024
Certificates of Deposit [Member]
Adjusted Cost	1,600
Total Fair Value	1,600
Fair Value of Investments in Unrealized Loss Position
Auction Rate Securities [Member]
Adjusted Cost	5,570	5,570
Total Fair Value	5,257	5,256
Unrealized Losses	(313)	(314)
Fair Value of Investments in Unrealized Loss Position	$ 5,257	$ 5,256

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

No definition available.

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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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