Note 11 - Segment and Enterprise-wide Disclosures - Net Sales to Unaffiliated Customers by Geography (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net sales	$ 30,170	$ 29,100	$ 29,483	$ 28,479	$ 28,389	$ 24,165	$ 27,020	$ 25,994	$ 117,232	$ 105,568	$ 100,867
UNITED STATES
Net sales									63,130	59,078	58,470
GERMANY
Net sales									12,400	12,445	11,576
Other Countries [Member]
Net sales									$ 41,702	$ 34,045	$ 30,821