Note 6 - Business Segments and Sales of Products - Sales by Geographic Area (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Sales by geographical area	$ 132,879	$ 144,563	$ 287,972	$ 283,657
CANADA
Sales by geographical area	78,158	94,524	171,030	183,192
KOREA, REPUBLIC OF
Sales by geographical area	26,202	41,537	75,501	74,240
JAPAN
Sales by geographical area	9,236	3,897	17,585	17,670
NETHERLANDS
Sales by geographical area	16,055	0	16,055	0
CHINA
Sales by geographical area	0	198	0	67
UNITED STATES
Sales by geographical area	$ 3,228	$ 4,407	$ 7,801	$ 8,488