Note 1 - Summary of Significant Interim Accounting Policies - Impact of New Standard on Statement of Comprehensive Income (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Net sales	$ 73,087,000	$ 60,987,000
Cost of goods sold	48,212,000	38,773,000
Selling and administrative expenses	21,182,000	$ 17,429,000
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Net sales	69,358,000
Cost of goods sold	45,496,000
Selling and administrative expenses	21,114,000
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Net sales	3,729,000
Cost of goods sold	2,716,000
Selling and administrative expenses	$ 68,000