Note 11 - Stock-based Compensation - Summary of Option Activity Under the Plans (Details) - $ / shares	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Outstanding, shares (in shares)	4,887,000
Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 7.57
Outstanding, Weighted Average Remaining Contractual Life (Year)	6 years 105 days		5 years 295 days
Granted, shares (in shares)	941,000
Granted, Weighted Average Exercise Price (in dollars per share)	$ 11.30
Exercised, shares (in shares)	(35,000)	0
Exercised, Weighted Average Exercise Price (in dollars per share)	$ 6.62
Cancelled, shares (in shares)	(46,000)
Cancelled, Weighted Average Exercise Price (in dollars per share)	$ 6.36
Expired, shares (in shares)	(28,000)
Expired, Weighted Average Exercise Price (in dollars per share)	$ 26.66
Outstanding, shares (in shares)	5,719,000		4,887,000
Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 8.11		$ 7.57
Exercisable, shares (in shares)	3,889,000
Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 7.96
Exercisable, Weighted Average Remaining Contractual Life (Year)	4 years 313 days
Vested and expected to vest, shares (in shares)	5,285,000
Vested and expected to vest, Weighted Average Exercise Price (in dollars per share)	$ 8.04
Vested and expected to vest, Weighted Average Remaining Contractual Life (Year)	6 years 10 days