Note 4 - Earnings Per Common Share - Basic and Diluted Earnings Per Common Share (Details) (Parentheticals)	Sep. 30, 2017	Aug. 31, 2017	Sep. 30, 2016	Mar. 31, 2016
1.625% Convertible Senior Notes due May 2018 [Member]
Interest rate	1.625%		1.625%	1.625%
0.25% Convertible Senior Notes Due June 2019 [Member]
Interest rate	0.25%		0.25%
1.25% Convertible Senior Notes Due August 2032 [Member]
Interest rate	1.25%	1.25%	1.25%