Note 5 - Benefit Plans - Stock Option Activity (Details)	3 Months Ended
	Mar. 31, 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	5.28
Forfeited, weighted average exercise price (in dollars per share) | $ / shares	28.71
Balance outstanding, weighted average exercise price (in dollars per share) | $ / shares	6.37
Options exercisable, weighted average exercise price (in dollars per share) | $ / shares	$ 6.37
Incentive Stock Options [Member]
Balance outstanding (in shares)	46,000
Granted (in shares)
Exercised (in shares)	(4,500)
Forfeited (in shares)	(20,000)
Balance outstanding (in shares)	21,500
Options exercisable (in shares)	21,500
Non-Incentive Stock Options [Member]
Balance outstanding (in shares)	25,000
Granted (in shares)
Exercised (in shares)
Forfeited (in shares)	(10,000)
Balance outstanding (in shares)	15,000
Options exercisable (in shares)	15,000