Note 2 - Summary of Significant Accounting Policies - Credit Concentration (Details) - Customer Concentration Risk [Member]	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Customer A [Member] | Revenue from Contract with Customer Benchmark [Member]
Credit concentration	43.00%	39.00%
Customer X [Member] | Accounts Receivable [Member]
Credit concentration	25.00%	12.00%
Customer B [Member] | Revenue from Contract with Customer Benchmark [Member]
Credit concentration		18.00%
Customer B [Member] | Revenue from Contract with Customer Benchmark [Member] | Maximum [Member]
Credit concentration	10.00%
Customer Y [Member] | Accounts Receivable [Member]
Credit concentration	10.00%	31.00%
Customer C [Member] | Revenue from Contract with Customer Benchmark [Member]
Credit concentration		10.00%
Customer C [Member] | Revenue from Contract with Customer Benchmark [Member] | Maximum [Member]
Credit concentration	26.00%
Customer Z [Member] | Accounts Receivable [Member]
Credit concentration	11.00%	10.00%
Customer D [Member] | Revenue from Contract with Customer Benchmark [Member]
Credit concentration	10.00%	18.00%