Note 6 - Stock Based Compensation - Stock Option Activity (Details) - 2005 Stock Option Plan [Member]	6 Months Ended
	Jun. 30, 2017 USD ($) $ / shares shares
Beginning balance, options outstanding (in shares) | shares	201,000
Beginning balance, weighted average exercise price (in dollars per share) | $ / shares	$ 7.80
Exercised, options outstanding (in shares) | shares	(2,000)
Exercised, weighted average exercise price (in dollars per share) | $ / shares	$ 6.90
Expired, options outstanding (in shares) | shares
Ending balance, weighted average exercise price (in dollars per share) | $ / shares	$ 7.81
Balance, aggregate intrinsic value | $	$ 605,017	[1]
Expired, weighted average exercise price (in dollars per share) | $ / shares
Forfeited, options outstanding (in shares) | shares
Forfeited, weighted average exercise price (in dollars per share) | $ / shares
Ending balance, options outstanding (in shares) | shares	199,000
Balance, weighted average contractual term (Year)	6 years
Exercisable, options outstanding (in shares) | shares	107,200
Exercisable, weighted average exercise price (in dollars per share) | $ / shares	$ 8.59
Exercisable, aggregate intrinsic value | $	$ 251,577	[1]
Exercisable, weighted average contractual term (Year)	4 years 266 days

[1] The aggregate intrinsic value of a stock option in the table above represents the total pre-tax intrinsic value (the amount by which the current market value of the underlying stock exceeds the exercise price of the option) that would have been received by the option holders had all option holders exercised their options on June 30, 2017.