Note 13 - Dividends Declared (Details) - USD ($) $ / shares in Units, $ in Thousands	May 31, 2016	May 06, 2016	Feb. 05, 2016	Nov. 06, 2015	Aug. 10, 2015	May 12, 2015	Feb. 11, 2015	Nov. 12, 2014	Aug. 14, 2014
Dividends Per Share of Common Stock (in dollars per share)		$ 0.50	$ 0.44	$ 0.44	$ 0.44	$ 0.44	$ 0.39	$ 0.39	$ 0.39
Record Date		May 31, 2016	Feb. 29, 2016	Nov. 30, 2015	Aug. 31, 2015	May 29, 2015	Feb. 27, 2015	Nov. 28, 2014	Aug. 29, 2014
Dividends, Cash	$ 20,200	$ 20,171	$ 18,044	$ 18,208	$ 18,179	$ 18,274	$ 16,236	$ 16,216	$ 16,299
Payment Date		Jun. 21, 2016	Mar. 15, 2016	Dec. 15, 2015	Sep. 15, 2015	Jun. 16, 2015	Mar. 17, 2015	Dec. 16, 2014	Sep. 16, 2014