Note 11 - Stock-based Compensation - Restricted Stock Activity (Details) - Restricted Stock [Member]	6 Months Ended
	Jun. 30, 2020 $ / shares shares
Outstanding, shares (in shares) | shares	712,496
Outstanding, grant date fair value (in dollars per share) | $ / shares	$ 23.66
Granted, shares (in shares) | shares	63,158
Granted, grant date fair value (in dollars per share) | $ / shares	$ 8.11
Vested, shares (in shares) | shares	(106,779)
Vested, grant date fair value (in dollars per share) | $ / shares	$ 19.45
Canceled or forfeited, shares (in shares) | shares	(22,361)
Canceled or forfeited, grant date fair value (in dollars per share) | $ / shares	$ 25.56
Outstanding, shares (in shares) | shares	646,514
Outstanding, grant date fair value (in dollars per share) | $ / shares	$ 22.77