Note 2 - Stock-based Compensation - Stock Incentive Plan Activities (Details) - Incentive Plan [Member] shares in Thousands	9 Months Ended
	Sep. 30, 2017 $ / shares shares
Awards available, beginning balance (in shares)	2,273
Options outstanding, beginning balance (in shares)	12,095
Weighted average exercise price, beginning balance (in dollars per share) | $ / shares	$ 6.55
Awards available, plan amendment (in shares)	1,000
Awards available, stock option awards granted (in shares)	(2,591)
Options outstanding, stock option awards granted (in shares)	2,591
Weighted average exercise price, stock option awards granted (in dollars per share) | $ / shares	$ 5.49
Options outstanding, stock option awards exercised (in shares)	(422)
Weighted average exercise price, stock option awards exercised (in dollars per share) | $ / shares	$ 3.49
Awards available, stock option awards cancelled (in shares)	912
Options outstanding, stock option awards cancelled (in shares)	(912)
Weighted average exercise price, stock option awards cancelled (in dollars per share) | $ / shares	$ 10.22
Awards available, ending balance (in shares)	1,581
Options outstanding, ending balance (in shares)	13,352
Weighted average exercise price, ending balance (in dollars per share) | $ / shares	$ 6.19
Restricted Stock Units (RSUs) [Member]
Awards available, restricted stock unit awards granted (in shares)	(16)
Awards available, restricted stock unit awards cancelled (in shares)	3