Note 7 - Business Segments and Sales of Products - Sales by Geographic Area (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Sales by geographical area	$ 138,627	$ 141,465	$ 422,284	$ 421,574
CANADA
Sales by geographical area	83,723	79,834	266,915	263,268
KOREA, REPUBLIC OF
Sales by geographical area	35,796	27,396	110,036	75,339
JAPAN
Sales by geographical area	3,301	14,419	20,971	38,513
CHINA
Sales by geographical area		16,695	66	32,047
UNITED STATES
Sales by geographical area	$ 15,807	$ 3,121	$ 24,296	$ 12,407