Note 6 - Business Segments and Sales of Products - Sales by Geographic Area (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Sales by geographical area	$ 139,094	$ 146,637
CANADA
Sales by geographical area	88,668	100,219
KOREA, REPUBLIC OF
Sales by geographical area	32,703	28,971
JAPAN
Sales by geographical area	13,773	12,290
UNITED STATES
Sales by geographical area	4,081	5,205
Other Geographic Areas [Member]
Sales by geographical area	$ (131)	$ (48)