Note 12 - Equity Incentive Plan - Summary of Exercisable Options and SAR's (Details)	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Incentive Stock Options [Member]
Exercisable Options and SAR's outstanding (in shares) | shares	182,472
Exercisable Options and SAR's, Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 14.12
Exercisable Options and SAR's, Weighted Average Remaining Term (Year)	4 years 109 days
Non-qualified Stock Options [Member]
Exercisable Options and SAR's outstanding (in shares) | shares	374,211
Exercisable Options and SAR's, Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 20.18
Exercisable Options and SAR's, Weighted Average Remaining Term (Year)	5 years 109 days
Performance Shares [Member]
Exercisable Options and SAR's outstanding (in shares) | shares	32,598
Exercisable Options and SAR's, Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 38.79
Exercisable Options and SAR's, Weighted Average Remaining Term (Year)	7 years 255 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)	2 years 36 days