Note 11 - Stockholders' Equity - Summary of Stock Option Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Balance, outstanding (in shares)	56,400	68,400	72,400
Balance, outstanding (in dollars per share)	$ 5.14	$ 5.17	$ 5.16
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	0	0	0
Granted (in dollars per share)
Forfeited or cancelled (in shares)	(12,000)	(12,000)	(2,000)
Forfeited or cancelled (in dollars per share)	$ 5.14	$ 5.30	$ 4.96
Exercised (in shares)	(44,400)		(2,000)
Exercised (in dollars per share)	$ 5.14		$ 4.96
Balance, outstanding (in shares)		56,400	68,400
Balance, outstanding (in dollars per share)		$ 5.14	$ 5.17
Exercisable at end of year (in shares)		56,400	68,400
Exercisable at end of year (in dollars per share)		$ 5.14	$ 5.17
Weighted-average fair value of options granted during year (in dollars per share)