Note 13 - Stock-based Compensation - Options Outstanding by Exercise Price Range (Details)	6 Months Ended
	Jun. 30, 2018 $ / shares shares
Options outstanding (in shares) | shares	1,297,121
Weighted average exercise price (in dollars per share)	$ 70.84
Weighted average remaining contractual life in years (Year)	3 years 219 days
Exercise Price Range 1 [Member]
Options outstanding (in shares) | shares	218,846
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)	$ 59.77
Weighted average remaining contractual life in years (Year)	2 years 328 days
Exercise Price Range 2 [Member]
Options outstanding (in shares) | shares	1,078,275
Weighted average exercise price (in dollars per share)	$ 72.94
Weighted average remaining contractual life in years (Year)	3 years 255 days