Note 13 - Employee Benefit Plans - Stock Option Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Balance outstanding, weighted average exercise price (in dollars per share)	$ 19.95	$ 19.58	$ 18.23
Granted, weighted average exercise price (in dollars per share)
Exercised, weighted average exercise price (in dollars per share)	5.19	5.20	5.22
Forfeited, weighted average exercise price (in dollars per share)	$ 29.48	28.34	25.19
Balance outstanding (in shares)	71,000
Balance outstanding, weighted average exercise price (in dollars per share)	$ 15.74	$ 19.95	$ 19.58
Options exercisable, weighted average exercise price (in dollars per share)	$ 15.74
Incentive Stock Options [Member]
Balance outstanding (in shares)	60,000	91,500	140,300
Granted (in shares)
Exercised (in shares)	(3,000)	(11,500)	(10,800)
Forfeited (in shares)	(11,000)	(20,000)	(38,000)
Balance outstanding (in shares)	46,000	60,000	91,500
Options exercisable (in shares)	46,000
Non-Incentive Stock Options [Member]
Balance outstanding (in shares)	50,000	57,500	82,500
Granted (in shares)
Exercised (in shares)		(5,000)	(25,000)
Forfeited (in shares)	(25,000)	(2,500)
Balance outstanding (in shares)	25,000	50,000	57,500
Options exercisable (in shares)	25,000