Note 12 - Business Segments, Sales of Products and Significant Customers - Sales by Geographic Area (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Sales by geographical area	$ 559,053	$ 583,758	$ 660,193
UNITED STATES
Sales by geographical area	48,437	16,806	22,499
CANADA
Sales by geographical area	322,402	358,663	437,621
JAPAN
Sales by geographical area	42,885	58,475	44,158
KOREA, REPUBLIC OF
Sales by geographical area	145,263	80,183	116,687
CHINA
Sales by geographical area	66	69,631	35,220
Other Geographic Areas [Member]
Sales by geographical area			$ 4,008