Note 3 - Investments (Details Textual) - USD ($)	3 Months Ended
Mar. 31, 2019	Dec. 31, 2018
Available-for-sale Securities, Amortized Cost Basis, Total	$ 7,293,495	$ 9,806,866
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0	0
Certificates of Deposit [Member]
Available-for-sale Securities, Amortized Cost Basis, Total	700,000	900,000
Money Market Funds [Member]
Available-for-sale Securities, Amortized Cost Basis, Total	664,549	454,224
Available-for-sale Securities, Total	665,000	454,000
Corporate Bond Securities [Member]
Available-for-sale Securities, Amortized Cost Basis, Total	5,928,995	$ 8,452,701
Investment Owned, at Fair Value	$ 5,919,000
Weighted Average Yield to Book Value of Investment Grade Corporate Bonds	3.28%
Weighted Average Maturity of Investment	4 years 277 days
Corporate Bond Securities [Member] \| BBB- or Better [Member]
Investment Owned, at Fair Value	$ 5,710,000
Corporate Bond Securities [Member] \| BB + or Lower [Member]
Investment Owned, at Fair Value	$ 209,000

Represents the weighted average maturity of the investment.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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No definition available.

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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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No definition available.

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This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for twelve months or longer.

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No definition available.

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Value of the investment at close of period. For schedules of investments that are categorized, the value would be aggregated by category. For investment in and advances to affiliates, if operations of any controlled companies are different in character from those of the company, group such affiliates within divisions and by type of activities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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-Topic 946
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