Note 9 - Benefit Plans - Stock Option Activity (Details)	3 Months Ended
	Mar. 31, 2019 $ / shares shares
Balance outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 5.14
Granted, weighted average exercise price (in dollars per share) | $ / shares
Exercised, weighted average exercise price (in dollars per share) | $ / shares	5.19
Forfeited, weighted average exercise price (in dollars per share) | $ / shares
Balance outstanding, weighted average exercise price (in dollars per share) | $ / shares	5.08
Options exercisable, weighted average exercise price (in dollars per share) | $ / shares	$ 5.08
Incentive Stock Options [Member]
Balance outstanding (in shares)	12,500
Granted (in shares)
Exercised (in shares)	(7,500)
Forfeited (in shares)
Balance outstanding (in shares)	5,000
Options exercisable (in shares)	5,000
Non-Incentive Stock Options [Member]
Balance outstanding (in shares)	5,000
Granted (in shares)
Exercised (in shares)	(2,500)
Forfeited (in shares)
Balance outstanding (in shares)	2,500
Options exercisable (in shares)	2,500