Note 13 - Stock-based Compensation - Options Outstanding by Exercise Price Range (Details)	3 Months Ended
	Mar. 31, 2020 $ / shares shares
Options outstanding (in shares) | shares	835,227
Weighted average exercise price (in dollars per share)	$ 72.20
Weighted average remaining contractual life (Year)	2 years 3 days
Exercise Price Range 1 [Member]
Options outstanding (in shares) | shares	133,958
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)	$ 61.80
Weighted average remaining contractual life (Year)	1 year 9 months 25 days
Exercise Price Range 2 [Member]
Options outstanding (in shares) | shares	701,269
Exercise price, lower range (in dollars per share)	$ 72.94
Exercise price, upper range (in dollars per share)	86.48
Weighted average exercise price (in dollars per share)	$ 74.19
Weighted average remaining contractual life (Year)	2 years 18 days