Note 8 - Treasury Shares (Details Textual) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended						9 Months Ended	81 Months Ended
	Aug. 01, 2018	Aug. 12, 2016	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2013	Dec. 31, 2012
Stock Repurchase Program, Number of Shares Authorized to be Repurchased		1,500,000										1,000,000	500,000
Stock Repurchase Program, Additional Shares Authorized		500,000
Treasury Stock, Shares, Ending Balance			1,203,491						1,203,491	1,203,491	1,090,370
Treasury Stock Acquired, Average Cost Per Share										$ 4.72
Treasury Stock, Value, Acquired, Cost Method			$ 706	$ 46	$ 36					$ 5,700
Treasury Stock, Shares, Acquired	100,000								113,121