Note 4 - Stock-based Compensation - Stock Options Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Options Outstanding, Number, beginning of period (in shares)		3,000	76,000
Options Outstanding, Weighted average exercise price, beginning of period (in dollars per share)		$ 12.79	$ 14.73
Options Outstanding, Weighted average remaining contractual term (Year)			146 days	182 days
Options Outstanding, Aggregate Intrinsic Value			$ 15	$ 945
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	0	0	0
Options Granted, Weighted average exercise price (in dollars per share)
Options Exercised, Number (in shares)		(3,000)	(73,000)
Options Exercised, Weighted average exercise price (in dollars per share)		$ 12.79	$ 14.79
Options Forfeited, Number (in shares)
Options forfeited, Weighted average exercise price (in dollars per share)
Options Outstanding, Number, end of period (in shares)			3,000	76,000
Options Outstanding, Weighted average exercise price (in dollars per share)			$ 12.79	$ 14.73
Options Exercisable, Number (in shares)