Note 3 - Stock-based Compensation - Activity Related to Restricted Stock Units Awarded (Details) - Restricted Stock [Member]	3 Months Ended
	Mar. 31, 2020 $ / shares shares
Nonvested (in shares) | shares	61,040
Nonvested, weighted average grant date fair value per share (in dollars per share) | $ / shares	$ 21.73
Granted (in shares) | shares	23,648
Granted, weighted average grant date fair value per share (in dollars per share) | $ / shares	$ 26.09
Nonvested (in shares) | shares	84,688
Nonvested, weighted average grant date fair value per share (in dollars per share) | $ / shares	$ 22.94
Expected to vest as of March 31, 2020 (in shares) | shares	1,000
Expected to vest as of March 31, 2020 (in dollars per share) | $ / shares	$ 22.65