Note 14 - Stock-based Compensation - Options Outstanding by Exercise Price Range (Details)	6 Months Ended
	Jun. 30, 2020 $ / shares shares
Options outstanding (in shares) | shares	853,421
Weighted average exercise price (in dollars per share)	$ 72.10
Weighted average remaining contractual life (Year)	1 year 8 months 19 days
Exercise Price Range 1 [Member]
Options outstanding (in shares) | shares	155,000
Exercise price, lower range (in dollars per share)	$ 60.73
Exercise price, upper range (in dollars per share)	64.64
Weighted average exercise price (in dollars per share)	$ 62.67
Weighted average remaining contractual life (Year)	2 years 9 months 3 days
Exercise Price Range 2 [Member]
Options outstanding (in shares) | shares	698,421
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)	$ 74.20
Weighted average remaining contractual life (Year)	1 year 9 months 18 days