Note 7 - Net Income (Loss) Per Share - Calculations of Net Income (Loss) Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Basic:
Net income (loss)	$ (9,911)	$ (16,008)	$ 36,093	$ 21,663	$ (25,919)	$ 57,756
Basic (in shares)	20,720		20,628		20,703	20,606
Basic (in dollars per share)	$ (0.48)		$ 1.75		$ (1.25)	$ 2.80
Diluted:
Net income (loss)	$ (9,911)	$ (16,008)	$ 36,093	$ 21,663	$ (25,919)	$ 57,756
Basic (in shares)	20,720		20,628		20,703	20,606
Unvested restricted stock and DSU's (in shares)			30
Employee stock options (in shares)
Diluted (in shares)	20,720		20,658		20,703	20,606
Diluted (in dollars per share)	$ (0.48)		$ 1.75		$ (1.25)	$ 2.80