Note 5 - Benefit Plans - Stock Option Activity (Details)	6 Months Ended
	Jun. 30, 2017 $ / shares shares
Balance outstanding (in dollars per share) | $ / shares	$ 20.15
Granted (in dollars per share) | $ / shares
Exercised (in dollars per share) | $ / shares
Balance outstanding (in dollars per share) | $ / shares	15.93
Options exercisable as of June 30, 2017 (in dollars per share) | $ / shares	15.93
Forfeited (in dollars per share) | $ / shares	$ 29.49
Incentive Stock Options [Member]
Balance outstanding (in shares)	60,000
Granted (in shares)
Exercised (in shares)
Options exercisable as of June 30, 2017 (in shares)	50,000
Forfeited (in shares)	(10,000)
Balance outstanding (in shares)	50,000
Non Incentive Stock Options [Member]
Balance outstanding (in shares)	52,500
Granted (in shares)
Exercised (in shares)
Options exercisable as of June 30, 2017 (in shares)	27,500
Forfeited (in shares)	(25,000)
Balance outstanding (in shares)	27,500