Note 6 - Share-based Payments - Summary of Stock Option Activity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Outstanding, Beginning of Year (in shares)		12,750
Outstanding, Beginning of Year, average exercise price (in dollars per share)		$ 24.93
Exercised (in shares)		10,250
Exercised, average exercise price (in dollars per share)		$ 24.93
Forfeited or Expired (in shares)		2,500
Forfeited or Expired, average exercise price (in dollars per share)		$ 24.93
Outstanding, End of Year (in shares)
Outstanding, End of Year, average exercise price (in dollars per share)
Exercisable, End of Year (in shares)
Exercisable, End of Year, average exercise price (in dollars per share)
Cash Received for Options Exercised, average exercise price		$ 256,000
Intrinsic Value of Options Exercised, average exercise price		$ 75,000