Note 3 - Earnings Per Share - Schedule of Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net income (loss)									$ 11,352	$ (8,661)	$ 4,864
Weighted average shares outstanding
Total weighted average shares outstanding, basic (in shares)									45,378,188	44,576,912	45,649,971
Dilutive potential common shares (in shares)									961,866	0	806,950
Total weighted average shares outstanding, diluted (in shares)									46,340,054	44,576,912	46,456,921
Net income (loss) per share available to common stockholders
Basic (in dollars per share)									$ 0.25	$ (0.19)	$ 0.11
Diluted (in dollars per share)	$ (0.10)	$ 0.11	$ 0	$ 0.24	$ (0.36)	$ 0.20	$ (0.06)	$ 0.01	$ 0.24	$ (0.19)	$ 0.10