Note 1 - Summary of Significant Accounting Policies - Impact of New Standard on Statement of Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	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, 2018	Dec. 31, 2017	Dec. 31, 2016
Net sales	$ 95,001	$ 95,870	$ 82,392	$ 73,087	$ 72,450	$ 67,773	$ 65,604	$ 60,987	$ 64,686	$ 65,282	$ 64,660	$ 57,968	$ 346,350	$ 266,814	$ 252,596
Cost of goods sold													224,653	170,462	165,614
Selling and administrative expenses													96,710	$ 70,592	$ 65,124
Accounting Standards Update 2014-09 [Member]
Net sales													42,880
Cost of goods sold													27,397
Selling and administrative expenses													706
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Net sales													342,881
Cost of goods sold													221,920
Selling and administrative expenses													96,758
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Net sales													3,469
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Net sales													3,469
Cost of goods sold													2,733
Selling and administrative expenses													$ (48)