Note 9 - Stockholders' Equity - Summary of RSU Activity (Details) - Restricted Stock Units (RSUs) [Member]	12 Months Ended
	Dec. 31, 2018 $ / shares shares
Outstanding (in shares) | shares	216,750
Outstanding, weighted average grant date fair value (in dollars per share) | $ / shares	$ 18.10
Granted (in shares) | shares	87,088
Granted, weighted average grant date fair value (in dollars per share) | $ / shares	$ 23.65
Vested (in shares) | shares	(63,478)	[1]
Vested, weighted average grant date fair value (in dollars per share) | $ / shares	$ 15.11	[1]
Canceled (in shares) | shares	(22,465)
Canceled, weighted average grant date fair value (in dollars per share) | $ / shares	$ 17.75
Outstanding (in shares) | shares	217,895
Outstanding, weighted average grant date fair value (in dollars per share) | $ / shares	$ 21.21

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