Note 3 - Concentration of Credit Risk (Details Textual)	3 Months Ended	6 Months Ended	12 Months Ended
Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Cash and Cash Equivalents, at Carrying Value, Ending Balance	$ 8,580,564	$ 15,396,489	$ 8,580,564	$ 15,396,489	$ 11,439,361	$ 14,210,909
Cash Equivalents, at Carrying Value, Total	7,500,000		7,500,000		8,900,000
Cash, Uninsured Amount	$ 6,824,000		$ 6,824,000		$ 6,920,000
Customer Concentration Risk [Member] \| Revenue Benchmark [Member]
Number Of Major Customers	1		1
Concentration Risk, Percentage	13.00%	37.00%	10.00%	43.00%
Customer Concentration Risk [Member] \| Accounts Receivable [Member]
Number Of Major Customers			2		2
Concentration Risk, Percentage			24.00%		42.00%

Number of major customers.

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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

+ References

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Amount of short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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The amount of cash as of the balance sheet date that is not insured by the Federal Deposit Insurance Corporation.

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- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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