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Note 5 - Cash Equivalents and Marketable Securities - Held to Maturity Securities (Details) - Municipal Bonds [Member]
Sep. 30, 2017
USD ($)
Held to maturity, cost $ 412,366
Held to maturity, accrued interest 6,986
Held to maturity, amortization bond premium 59,099
Held to maturity, amortized cost 360,253
Held to maturity, unrealized losses 216
Held to maturity, estimated fair value $ 360,469