Note 10 - Stockholders' Equity - Summary of RSU Activity (Details) - Restricted Stock Units (RSUs) [Member]	12 Months Ended
	Dec. 31, 2020 $ / shares shares
Outstanding (in shares) | shares	188,681
Outstanding, weighted average grant date fair value (in dollars per share) | $ / shares	$ 26.14
Granted (in shares) | shares	46,146
Granted, weighted average grant date fair value (in dollars per share) | $ / shares	$ 36.86
Vested (in shares) | shares	(50,669)	[1]
Vested, weighted average grant date fair value (in dollars per share) | $ / shares	$ 22.76	[1]
Canceled (in shares) | shares	(37,143)
Canceled, weighted average grant date fair value (in dollars per share) | $ / shares	$ 27.88
Outstanding (in shares) | shares	147,015
Outstanding, weighted average grant date fair value (in dollars per share) | $ / shares	$ 30.24

[1] The number of RSUs vested includes the shares that we withheld on behalf of employees to satisfy minimum statutory tax withholding requirements. The fair values of the RSUs that vested during 2020, 2019 and 2018 were $1.8 million, $2.1 million, and $1.9 million, respectively.