Note 11 - Stock-based Compensation - Restricted Stock Activity (Details) - Restricted Stock [Member]	12 Months Ended
	Dec. 31, 2019 $ / shares shares
Outstanding, shares (in shares) | shares	287,479
Outstanding, grant date fair value (in dollars per share) | $ / shares	$ 29.26
Granted, shares (in shares) | shares	709,205
Granted, grant date fair value (in dollars per share) | $ / shares	$ 19.37
Vested, shares (in shares) | shares	(231,543)
Vested, grant date fair value (in dollars per share) | $ / shares	$ 17.19
Canceled or forfeited, shares (in shares) | shares	(52,645)
Canceled or forfeited, grant date fair value (in dollars per share) | $ / shares	$ 24.78
Outstanding, shares (in shares) | shares	712,496
Outstanding, grant date fair value (in dollars per share) | $ / shares	$ 23.66