Note 15 - Supplemental Cash Flow Information (Details Textual) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock Repurchased During Period, Shares	50,981	27,770	14,571
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	336,726	279,766
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	144,443	81,608	50,224