Note 2 - Summary of Significant Accounting Policies - Credit Concentration (Details) - Customer Concentration Risk [Member]	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Customer A [Member] \| Revenue from Contract with Customer [Member]
Credit concentration	39.00%	28.00%
Customer A [Member] \| Accounts Receivable [Member]
Credit concentration	23.00%		12.00%
Customer B [Member] \| Revenue from Contract with Customer [Member]
Credit concentration		17.00%
Customer B [Member] \| Revenue from Contract with Customer [Member] \| Maximum [Member]
Credit concentration	10.00%
Customer B [Member] \| Accounts Receivable [Member]
Credit concentration			19.00%
Customer B [Member] \| Accounts Receivable [Member] \| Maximum [Member]
Credit concentration	10.00%
Customer C [Member] \| Revenue from Contract with Customer [Member]
Credit concentration		12.00%
Customer C [Member] \| Revenue from Contract with Customer [Member] \| Maximum [Member]
Credit concentration	10.00%
Customer C [Member] \| Accounts Receivable [Member]
Credit concentration			12.00%
Customer C [Member] \| Accounts Receivable [Member] \| Maximum [Member]
Credit concentration	10.00%
Customer D [Member] \| Revenue from Contract with Customer [Member]
Credit concentration	18.00%
Customer D [Member] \| Revenue from Contract with Customer [Member] \| Maximum [Member]
Credit concentration		10.00%
Customer D [Member] \| Accounts Receivable [Member]
Credit concentration			10.00%
Customer D [Member] \| Accounts Receivable [Member] \| Maximum [Member]
Credit concentration	10.00%
Customer E [Member] \| Revenue from Contract with Customer [Member]
Credit concentration	18.00%
Customer E [Member] \| Revenue from Contract with Customer [Member] \| Maximum [Member]
Credit concentration		10.00%
Customer E [Member] \| Accounts Receivable [Member]
Credit concentration			10.00%
Customer E [Member] \| Accounts Receivable [Member] \| Maximum [Member]
Credit concentration	10.00%
Customer F [Member] \| Accounts Receivable [Member]
Credit concentration	13.00%
Customer F [Member] \| Accounts Receivable [Member] \| Maximum [Member]
Credit concentration			10.00%
Customer G [Member] \| Accounts Receivable [Member]
Credit concentration	11.00%
Customer G [Member] \| Accounts Receivable [Member] \| Maximum [Member]
Credit concentration			10.00%