Note 11 - Dividends (Details Textual) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Payments of Ordinary Dividends, Common Stock					$ 5,459	$ 4,361	$ 3,252
Paid Quarterly [Member]
Common Stock, Dividends, Per Share, Declared	$ 0.025	$ 0.025	$ 0.015	$ 0.015	$ 0.025		$ 0.015