Note 9 - Convertible Senior Notes (Details Textual) - Five Point Eight Seven Five Percent Convertible Senior Notes Due Two Thousand Thirty Five [Member] - Convertible Debt [Member] - USD ($) $ in Thousands	Nov. 30, 2005	Mar. 31, 2019	Dec. 31, 2018
Debt Instrument, Face Amount	$ 300,000	$ 88,280	$ 88,280
Debt Instrument, Interest Rate, Stated Percentage	5.875%
Debt Instrument, Maturity Date	Nov. 30, 2035