Note 7 - Marketable Securities (Details Textual) - USD ($)	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Proceeds from Sale and Maturity of Marketable Securities, Total			$ 11,359,973	$ 4,947,370
Debt and Equity Securities, Realized Gain (Loss), Total		$ 115,328	$ 247,499	$ 2,052

The cash inflow associated with the aggregate amount received by the entity through sale or maturity of marketable securities (held-to-maturity or available-for-sale) during the period.

No definition available.

Name:	us-gaap_ProceedsFromSaleAndMaturityOfMarketableSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration