Note 6 - Stock Options (Details) - Employee Stock Option [Member] - USD ($) shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Options outstanding, beginning of period (in shares)	98	440	1,031
Options outstanding, beginning of period, weighted average exercise price (in dollars per share)	$ 20.40	$ 19.08	$ 16.63
Options outstanding, beginning of period, weighted average remaining contractual term	18 days	313 days	1 year 244 days	2 years 127 days
Options outstanding, beginning of period, aggregate intrinsic value	$ 6.3	$ 25.6	$ 44.4
Options exercised (in shares)	(95)	(341)	(585)
Options exercised, weighted average exercise price (in dollars per share)	$ 20.35	$ 18.70	$ 14.77
Options exercised, aggregate intrinsic value	$ 5.8	$ 19.9	$ 34.0
Options forfeited (in shares)	(1)	(1)	(6)
Options forfeited, weighted average exercise price (in dollars per share)	$ 24.27	$ 19.08	$ 19.89
Options outstanding, end of period (in shares)	2	98	440	1,031
Options outstanding, end of period, weighted average exercise price (in dollars per share)	$ 20.76	$ 20.40	$ 19.08	$ 16.63
Options outstanding, end of period, aggregate intrinsic value	$ 0.1	$ 6.3	$ 25.6	$ 44.4
Options exercisable (in shares)	2
Options exercisable, weighted average exercise price (in dollars per share)	$ 20.76
Options exercisable, weighted average remaining contractual term	18 days
Options exercisable, aggregate intrinsic value	$ 0.1