Note 9 - Concentration of Credit Risk (Details Textual) - Customer Concentration Risk [Member]	3 Months Ended
	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)
Revenue Benchmark [Member]
Number of Major Customers	2	2
Revenue Benchmark [Member] | Customer One [Member]
Concentration Risk, Percentage	30.80%	31.80%
Revenue Benchmark [Member] | Customer Two [Member]
Concentration Risk, Percentage	17.20%	17.70%
Accounts Receivable [Member] | Customer One [Member]
Accounts Receivable, before Allowance for Credit Loss	$ 2,933,000	$ 3,643,000
Concentration Risk, Percentage	27.70%	33.40%
Accounts Receivable [Member] | Customer Two [Member]
Accounts Receivable, before Allowance for Credit Loss	$ 2,279,000	$ 2,657,000
Concentration Risk, Percentage	21.50%	24.30%