Note 11 - Stock-based Compensation - Summary of Option Activity Under the Plans (Details) - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Outstanding, shares (in shares)	5,535
Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 7.25
Outstanding, Weighted Average Remaining Contractual Life (Year)	6 years 7 days	6 years 14 days
Granted, shares (in shares)	1,566
Granted, Weighted Average Exercise Price (in dollars per share)	$ 6.93
Exercised, shares (in shares)	(96)
Exercised, Weighted Average Exercise Price (in dollars per share)	$ 4.85
Cancelled, shares (in shares)	(483)
Cancelled, Weighted Average Exercise Price (in dollars per share)	$ 7.97
Expired, shares (in shares)	(258)
Expired, Weighted Average Exercise Price (in dollars per share)	$ 16.05
Outstanding, shares (in shares)	6,264	5,535
Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 6.79	$ 7.25
Exercisable, shares (in shares)	4,242
Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 6.42
Exercisable, Weighted Average Remaining Contractual Life (Year)	4 years 284 days
Vested and expected to vest, shares (in shares)	5,887
Vested and expected to vest, Weighted Average Exercise Price (in dollars per share)	$ 6.75
Vested and expected to vest, Weighted Average Remaining Contractual Life (Year)	5 years 306 days