Note 10 - Stock-based Compensation Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Selling, General and Administrative Expenses [Member]
Stock-based compensation recognized in Consolidated Statements of Operations, as a component of selling, general and administrative expense (in millions)	$ 11.9	$ 7.4	$ 6.6
Per share intrinsic value of non-vested stock granted (in dollars per share)	$ 88.74	$ 68.99	$ 43.13
Weighted average per share discount from market value for shares purchased (in dollars per share)	$ 15.89	$ 11.92	$ 8.81
Total intrinsic value of stock options exercised (in millions)	$ 0.5	$ 3.1	$ 8.7
Fair value of non-vested stock that vested during the period (in millions)	19.3	18.9	8.4
Tax benefit recognized in Consolidated Statements of Operations (in millions)	4.2	2.6	2.3
Cash received from options exercised and shares purchased under all share-based arrangements (in millions)	6.5	4.9	5.2
Tax deduction realized related to stock options exercised (in millions)	$ 7.6	$ 8.4	$ 6.5