Note 15 - Stock-based Compensation - Options Outstanding by Exercise Price Range (Details)	12 Months Ended
	Dec. 31, 2018 $ / shares shares
Options outstanding (in shares) | shares	1,163,381
Weighted average exercise price (in dollars per share)	$ 71.16
Weighted average remaining contractual life (Year)	3 years 36 days
Exercise Price Range 1 [Member]
Options outstanding (in shares) | shares	175,106
Exercise price, lower range (in dollars per share)	$ 52.93
Exercise price, upper range (in dollars per share)	62.78
Weighted average exercise price (in dollars per share)	$ 61.10
Weighted average remaining contractual life (Year)	2 years 292 days
Exercise Price Range 2 [Member]
Options outstanding (in shares) | shares	988,275
Exercise price, lower range (in dollars per share)	$ 72.94
Exercise price, upper range (in dollars per share)	72.94
Weighted average exercise price (in dollars per share)	$ 72.94
Weighted average remaining contractual life (Year)	3 years 73 days