Note 11 - Stock-based Compensation - Summary of Option Activity Under the Plans (Details) - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Outstanding, shares (in shares)	6,264
Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 6.79
Outstanding, Weighted Average Remaining Contractual Life (Year)	6 years 32 days	6 years 7 days
Granted, shares (in shares)	2,060
Granted, Weighted Average Exercise Price (in dollars per share)	$ 4.78
Cancelled, shares (in shares)	(921)
Cancelled, Weighted Average Exercise Price (in dollars per share)	$ 6.35
Exercised, shares (in shares)	(386)
Exercised, Weighted Average Exercise Price (in dollars per share)	$ 5.03
Expired, shares (in shares)	(77)
Expired, Weighted Average Exercise Price (in dollars per share)	$ 6.22
Outstanding, shares (in shares)	6,940	6,264
Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 6.35	$ 6.79
Exercisable, shares (in shares)	4,660
Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 6.65
Exercisable, Weighted Average Remaining Contractual Life (Year)	4 years 281 days
Vested and expected to vest, shares (in shares)	6,440
Vested and expected to vest, Weighted Average Exercise Price (in dollars per share)	$ 6.43
Vested and expected to vest, Weighted Average Remaining Contractual Life (Year)	5 years 313 days