Note 10 - Convertible Senior Notes - Summary of Convertible Senior Notes (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Aug. 26, 2019	Nov. 30, 2005
Net carrying value	$ 24,091,000	$ 62,142,000
Five Point Eight Seven Five Percent Convertible Senior Notes Due Two Thousand Thirty Five [Member] | Convertible Debt [Member]
Face amount of convertible senior notes	33,839,000	88,280,000	$ 54,400,000	$ 300,000,000
Discount	(9,748,000)	(26,138,000)
Net carrying value	24,091,000	62,142,000
Carrying amount of equity component included in paid-in capital	108,714,000	108,714,000
Excess of instruments’ if-converted values over face principal amounts