Note 8 - Net Loss Per Share - Net Loss Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net income (loss)	$ (2,088)	$ (2,628)	$ 588	$ (8,220)	$ (26,293)	$ (873)	$ (1,572)	$ (2,032)	$ (12,348)	$ (30,770)	$ 29,993
Weighted average shares of common stock outstanding used in computing net income (loss) per share, basic (in shares)	14,261	14,182	14,086	14,017	13,932	13,851	13,709	13,587	14,096	13,771	13,873
Dilutive effect of incremental shares and share equivalents (in shares)											855
Weighted average shares of common stock outstanding used in computing net income (loss) per share, diluted (in shares)	14,261	14,182	14,356	14,017	13,932	13,851	13,709	13,587	14,096	13,771	14,728
Net income (loss) per share-basic (in dollars per share)	$ (0.15)	$ (0.19)	$ 0.04	$ (0.59)	$ (1.89)	$ (0.06)	$ (0.11)	$ (0.15)	$ (0.88)	$ (2.23)	$ 2.16
Net income (loss) per share-diluted (in dollars per share)	$ (0.15)	$ (0.19)	$ 0.04	$ (0.59)	$ (1.89)	$ (0.06)	$ (0.11)	$ (0.15)	$ (0.88)	$ (2.23)	$ 2.04