Note 18 - Foreign Operations and Sales - Sales to Geographic Area (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Gross sales	$ 175,505	$ 112,233	$ 134,487	$ 103,711	$ 178,682	$ 99,867	$ 119,054	$ 93,935	$ 525,936	$ 491,538	$ 433,856
Europe [Member]
Gross sales									327,309	321,525	280,593
North America [Member]
Gross sales									170,490	138,328	127,024
Asia [Member]
Gross sales									17,625	17,996	14,024
Other [Member]
Gross sales									$ 10,512	$ 13,689	$ 12,215