Note 8 - Benefit Plans - Stock Option Activity (Details)	6 Months Ended
	Jun. 30, 2018 $ / shares shares
Balance outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 15.74
Granted, weighted average exercise price (in dollars per share) | $ / shares
Exercised, weighted average exercise price (in dollars per share) | $ / shares	7.78
Forfeited, weighted average exercise price (in dollars per share) | $ / shares	28.71
Balance outstanding, weighted average exercise price (in dollars per share) | $ / shares	5.16
Options exercisable, weighted average exercise price (in dollars per share) | $ / shares	$ 5.16
Incentive Stock Options [Member]
Balance outstanding (in shares)	46,000
Granted (in shares)
Exercised (in shares)	(12,000)
Forfeited (in shares)	(20,000)
Balance outstanding (in shares)	14,000
Options exercisable (in shares)	14,000
Non-Incentive Stock Options [Member]
Balance outstanding (in shares)	25,000
Granted (in shares)
Exercised (in shares)	(5,000)
Forfeited (in shares)	(10,000)
Balance outstanding (in shares)	10,000
Options exercisable (in shares)	10,000