Note 14 - Stock-based Compensation - Stock Option Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Options outstanding, number of shares (in shares)	76,400	19,800
Options outstanding, weighted average exercise price (in dollars per share)	$ 5.98	$ 4.37
Granted, number of shares (in shares)	189,800	96,000
Granted, weighted average exercise price (in dollars per share)	$ 8.14	$ 6.35
Exercised, number of shares (in shares)
Canceled, number of shares (in shares)	(1,800)	(39,400)
Canceled, weighted average exercise price (in dollars per share)	$ 4.37	$ 6.08
Options outstanding, number of shares (in shares)	264,400	76,400