Note 14 - Stock-based Compensation - Summary of Outstanding Stock Options (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2016
Options outstanding, shares (in shares)	621,390	954,678	1,074,552
Options outstanding, weighted average exercise price (in dollars per share)	$ 48.15	$ 46.92	$ 46.44
Number of Shares - Options Granted (in shares)	56,291	56,210	57,716
Weighted Average Exercise Price - Options Granted (in dollars per share)	$ 62.54	$ 61.47	$ 53.10
Number of Shares - Options Exercised (in shares)	(499,066)	(389,498)	(157,590)
Weighted Average Exercise Price - Options Exercised (in dollars per share)	$ 47.16	$ 47.06	$ 45.97
Number of Shares - Options cancelled (in shares)	(656)		(20,000)
Weighted Average Exercise Price - Options cancelled (in dollars per share)	$ 46.69		$ 46.69
Options outstanding, shares (in shares)	177,959	621,390	954,678
Options outstanding, weighted average exercise price (in dollars per share)	$ 55.48	$ 48.15	$ 46.92
Options outstanding, shares (in shares)	621,390	954,678	1,074,552	177,959
Options outstanding, weighted average exercise price (in dollars per share)	$ 48.15	$ 46.92	$ 46.44	$ 55.48
Options outstanding				$ 3,615,000
Options exercisable (in shares)				177,959
Options exercisable, weighted average exercise price (in dollars per share)				$ 55.48
Options exercisable, aggregate intrinsic value				$ 3,615,000