Note 8 - Dividends Paid (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	[1]
Dividend amount per share (in dollars per share)	$ 0.20	$ 0.20	$ 0.20	$ 0.16	$ 0.16	$ 0.16	$ 0.16	$ 0.13	$ 0.13	$ 0.13	$ 0.13
Total amount of dividend	$ 5,246	$ 5,257	$ 5,266	$ 4,216	$ 4,198	$ 4,174	$ 4,179	$ 3,378	$ 3,366	$ 3,363	$ 3,356

[1] We declared and paid a dividend payment in December 2012 in lieu of the dividend typically declared and paid in March of the following year.