Note 9 - Stockholders' Equity - Summary of RSU Activity (Details) - Restricted Stock Units (RSUs) [Member]	12 Months Ended
	Dec. 31, 2019 $ / shares shares
Outstanding (in shares) | shares	217,895
Outstanding, weighted average grant date fair value (in dollars per share) | $ / shares	$ 21.21
Granted (in shares) | shares	56,567
Granted, weighted average grant date fair value (in dollars per share) | $ / shares	$ 35.41
Vested (in shares) | shares	(61,058)	[1]
Vested, weighted average grant date fair value (in dollars per share) | $ / shares	$ 18.46	[1]
Canceled (in shares) | shares	(24,723)
Canceled, weighted average grant date fair value (in dollars per share) | $ / shares	$ 22.19
Outstanding (in shares) | shares	188,681
Outstanding, weighted average grant date fair value (in dollars per share) | $ / shares	$ 26.14

[1] The number of RSUs vested includes the shares that we withheld on behalf of employees to satisfy minimum statutory tax withholding requirements.