Note 2 - Stock-based Compensation - Stock Incentive Plan Activities (Details) - Incentive Plan [Member] shares in Thousands	9 Months Ended
	Sep. 30, 2019 $ / shares shares
Awards available, beginning balance (in shares)	805
Options outstanding, beginning balance (in shares)	17,491
Weighted average exercise price, beginning balance (in dollars per share) | $ / shares	$ 6.49
Awards available, plan amendment (in shares)	4,000
Awards available, stock option awards granted (in shares)	(866)
Options outstanding, stock option awards granted (in shares)	866
Weighted average exercise price, stock option awards granted (in dollars per share) | $ / shares	$ 6.72
Options outstanding, stock option awards exercised (in shares)	(251)
Weighted average exercise price, stock option awards exercised (in dollars per share) | $ / shares	$ 3.75
Awards available, stock option awards cancelled (in shares)	124
Options outstanding, stock option awards cancelled (in shares)	(124)
Weighted average exercise price, stock option awards cancelled (in dollars per share) | $ / shares	$ 7.25
Awards available, ending balance (in shares)	4,063
Options outstanding, ending balance (in shares)	17,982
Weighted average exercise price, ending balance (in dollars per share) | $ / shares	$ 6.53