Note 3 - Marketable Securities and Time Deposits - Marketable Debt Securities by Contractual Maturities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Marketable debt securities, amortized cost	$ 112,885	$ 108,575
Marketable debt securities, estimated fair value	111,251	107,366
Debt Securities [Member]
Marketable debt securities, amortized cost	99,406	98,081
Marketable debt securities, unrealized gains	1	13
Marketable debt securities, unrealized losses	(1,636)	(1,222)
Marketable debt securities, estimated fair value	97,772	96,872
Debt Securities [Member] \| Due in One Year or Less [Member]
Marketable debt securities, amortized cost	27,442	19,239
Marketable debt securities, unrealized gains		3
Marketable debt securities, unrealized losses	(78)	(26)
Marketable debt securities, estimated fair value	27,364	19,216
Debt Securities [Member] \| Due after One Year to Five Years [Member]
Marketable debt securities, amortized cost	71,965
Marketable debt securities, unrealized gains	1
Marketable debt securities, unrealized losses	(1,558)
Marketable debt securities, estimated fair value	$ 70,408
Debt Securities [Member] \| Due After One Year to Six Years [Member]
Marketable debt securities, amortized cost		78,842
Marketable debt securities, unrealized gains		10
Marketable debt securities, unrealized losses		(1,196)
Marketable debt securities, estimated fair value		$ 77,656

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (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 (c)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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