Note 9 - Stock-based Compensation - Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Balance, number of shares (in shares)	60,000	60,000
Balance, weighted average exercise price per share (in dollars per share)	$ 8	$ 8
Balance, weighted average fair value at grant date (in dollars per share)			$ 0	$ 0
Balance, weighted average remaining contractual life (Year)	4 years 131 days	4 years 182 days	0 years
Balance, intrinsic value		$ 0	$ 0
Options granted, number of shares (in shares)	10,000		60,000
Options granted, weighted average exercise price per share (in dollars per share)	$ 6		$ 8
Options granted, intrinsic value			$ 0
Options exercised, number of shares (in shares)		0	0
Options exercised, weighted average exercise price per share (in dollars per share)		$ 0	$ 0
Options exercised, intrinsic value		$ 0	$ 0
Options expired, number of shares (in shares)		0
Options expired, weighted average exercise price per share (in dollars per share)		$ 0
Options expired, intrinsic value		$ 0	$ 0
Options granted, weighted average remaining contractual life (Year)	5 years
Options expired, weighted average exercise price per share (in dollars per share)		$ 0
Balance, number of shares (in shares)	70,000	60,000	60,000
Balance, weighted average exercise price per share (in dollars per share)	$ 7.71	$ 8	$ 8
Balance, intrinsic value			$ 0	$ 0