Note 17 - Stock-based Compensation - Performance-based Restricted Stock Units (Details) - $ / shares		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Shares available for future issuance (in shares)		302,727	303,000
Performance Shares [Member]
Vesting period (Year)		3 years
Shares available for future issuance (in shares)	[1]
Performance Shares [Member] | Executive Officer [Member]
Vesting period (Year)		3 years	3 years	3 years
Shares awarded, grant date weighted average cost (in dollars per share)		$ 35.66	$ 22.61	$ 20.02
Shares available for future issuance (in shares)		43,325	69,161	43,011

[1] Under the 2015 Omnibus Equity Compensation Plan, shares of stock are authorized for issuance as incentive and nonqualified stock options, SARs, restricted stock, and restricted stock units