Note 11 - Stock-based Compensation - Options Outstanding (Details)	9 Months Ended
	Sep. 30, 2016 $ / shares shares
Exercise Price Range 1 [Member]
Options outstanding (in shares) | shares	97,500
Exercise prices, lower range limit (in dollars per share)	$ 44.80
Exercise prices, upper range limit (in dollars per share)	52.93
Weighted average exercise price (in dollars per share)	$ 48.95
Weighted average remaining contractual life in years	1 year 255 days
Exercise Price Range 2 [Member]
Options outstanding (in shares) | shares	99,733
Exercise prices, lower range limit (in dollars per share)	$ 61.25
Exercise prices, upper range limit (in dollars per share)	62.78
Weighted average exercise price (in dollars per share)	$ 61.98
Weighted average remaining contractual life in years	3 years 255 days
Options outstanding (in shares) | shares	197,233
Weighted average exercise price (in dollars per share)	$ 55.55
Weighted average remaining contractual life in years	2 years 255 days