Note 2 - Summary of Significant Accounting Policies - Credit Concentration (Details) - Customer Concentration Risk [Member]	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Customer A [Member] | Revenue from Contract with Customer [Member]
Credit concentration	44.00%	26.00%
Customer A [Member] | Accounts Receivable [Member]
Credit concentration			10.00%
Customer A [Member] | Accounts Receivable [Member] | Maximum [Member]
Credit concentration	23.00%
Customer B [Member] | Revenue from Contract with Customer [Member]
Credit concentration		11.00%
Customer B [Member] | Revenue from Contract with Customer [Member] | Maximum [Member]
Credit concentration	12.00%
Customer B [Member] | Accounts Receivable [Member]
Credit concentration			10.00%
Customer B [Member] | Accounts Receivable [Member] | Maximum [Member]
Credit concentration	10.00%
Customer C [Member] | Revenue from Contract with Customer [Member]
Credit concentration		11.00%
Customer C [Member] | Revenue from Contract with Customer [Member] | Maximum [Member]
Credit concentration	10.00%
Customer C [Member] | Accounts Receivable [Member]
Credit concentration			10.00%
Customer C [Member] | Accounts Receivable [Member] | Maximum [Member]
Credit concentration	10.00%
Customer D [Member] | Accounts Receivable [Member]
Credit concentration			12.00%
Customer D [Member] | Accounts Receivable [Member] | Maximum [Member]
Credit concentration	10.00%
Customer E [Member] | Accounts Receivable [Member]
Credit concentration			19.00%
Customer E [Member] | Accounts Receivable [Member] | Maximum [Member]
Credit concentration	10.00%
Customer F [Member] | Accounts Receivable [Member]
Credit concentration	10.00%
Customer F [Member] | Accounts Receivable [Member] | Maximum [Member]
Credit concentration			12.00%
Customer G [Member] | Accounts Receivable [Member]
Credit concentration	10.00%
Customer G [Member] | Accounts Receivable [Member] | Maximum [Member]
Credit concentration			10.00%
Customer H [Member] | Accounts Receivable [Member]
Credit concentration	10.00%
Customer H [Member] | Accounts Receivable [Member] | Maximum [Member]
Credit concentration			10.00%