Note 2 - Accounting Standards and Significant Accounting Policies - Concentration of Credit Risk (Details) - Customer Concentration Risk [Member]	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Revenue Benchmark [Member]
Concentration risk, Customer revenue	100.00%	100.00%	100.00%	100.00%
Revenue Benchmark [Member] | Largest Customer [Member]
Concentration risk, Customer revenue	27.00%	26.70%	26.50%	25.00%
Revenue Benchmark [Member] | Second Largest Customer [Member]
Concentration risk, Customer revenue	25.20%	29.70%	25.80%	26.10%
Revenue Benchmark [Member] | Third Largest Customer [Member]
Concentration risk, Customer revenue	17.90%	7.50%	17.10%	5.10%
Revenue Benchmark [Member] | Forth Largest Customer [Member]
Concentration risk, Customer revenue	12.20%	10.80%	11.90%	15.20%
Revenue Benchmark [Member] | Other Customer [Member]
Concentration risk, Customer revenue	17.70%	25.30%	18.70%	28.60%
Accounts Receivable [Member]
Concentration risk, Customer revenue			100.00%		100.00%
Accounts Receivable [Member] | Largest Customer [Member]
Concentration risk, Customer revenue			53.20%		41.60%
Accounts Receivable [Member] | Second Largest Customer [Member]
Concentration risk, Customer revenue			13.00%		24.90%
Accounts Receivable [Member] | Third Largest Customer [Member]
Concentration risk, Customer revenue			8.70%		12.80%
Accounts Receivable [Member] | Forth Largest Customer [Member]
Concentration risk, Customer revenue			7.60%		11.20%
Accounts Receivable [Member] | Other Customer [Member]
Concentration risk, Customer revenue			17.50%		9.50%