Note 6 - Fair Values of Assets and Liabilities (Details Textual)	Dec. 31, 2019
The 5.875% Convertible Senior Notes Due 2035 [Member]
Debt Instrument, Interest Rate, Stated Percentage	5.875%

Contractual interest rate for funds borrowed, under the debt agreement.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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