Note 13 - Equity Incentive Plan - Summary of Exercisable Options and SAR's (Details)	12 Months Ended
	Dec. 31, 2018 $ / shares shares
Incentive Stock Options [Member]
Exercisable Options and SAR's outstanding (in shares) | shares	139,674
Exercisable Options and SAR's, Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 24.53
Exercisable Options and SAR's, Weighted Average Remaining Term (Year)	4 years 36 days
Non-qualified Stock Options [Member]
Exercisable Options and SAR's outstanding (in shares) | shares	453,790
Exercisable Options and SAR's, Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 40.74
Exercisable Options and SAR's, Weighted Average Remaining Term (Year)	3 years 73 days
Performance Shares [Member]
Exercisable Options and SAR's outstanding (in shares) | shares	100,963
Exercisable Options and SAR's, Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 40.72
Exercisable Options and SAR's, Weighted Average Remaining Term (Year)	3 years 36 days
Stock Appreciation Rights (SARs) [Member]
Exercisable Options and SAR's outstanding (in shares) | shares	35,250
Exercisable Options and SAR's, Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 6.36
Exercisable Options and SAR's, Weighted Average Remaining Term (Year)	1 year 36 days