Note 15 - Stock-based Compensation - Stock Option Plans (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation [Abstract]
Outstanding, shares (in shares)	513,554	587,961	623,176
Outstanding, Weighted average exercise price (in dollars per share)	$ 17.13	$ 14.83	$ 13.88
Granted, shares (in shares)	16,315	43,250	76,749
Granted, Weighted average exercise price (in dollars per share)	$ 44.02	$ 43.86	$ 22.92
Exercised, shares (in shares)	(60,127)	(114,100)	(111,423)
Exercised, Weighted average exercise price (in dollars per share)	$ 13.56	$ 15.12	$ 14.97
Forfeited, shares (in shares)	(170)	(3,557)	(541)
Forfeited, Weighted average exercise price (in dollars per share)	$ 16.81	$ 26.74	$ 18.36
Outstanding, shares (in shares)	469,572	513,554	587,961
Outstanding, Weighted average exercise price (in dollars per share)	$ 18.52	$ 17.13	$ 14.83
Exercisable, , shares (in shares)	358,270	354,269	385,372
Weighted-average grant date fair value (in dollars per share)	$ 14.68	$ 14.75	$ 7.31