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Note 11 - Capital Stock (Details Textual) - USD ($)			2 Months Ended	6 Months Ended		16 Months Ended
	May 15, 2018	Mar. 06, 2018	May 15, 2018	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Dec. 31, 2018	Aug. 03, 2018	May 04, 2018	Feb. 28, 2018	Feb. 22, 2018
Proceeds from Issuance of Common Stock					$ 150,000,000
Payments of Stock Issuance Costs				$ 450,515	$ 1,522,194
Common Stock, Shares Authorized									40,000,000
Preferred Stock, Shares Authorized				1,000,000		1,000,000	1,000,000		1,000,000
Class of Warrant or Right, Outstanding				105,556		105,556	105,556
Common Class A [Member]
Sale of Stock, Value, Available to Issue											$ 150,000,000
Sale of Stock, Price Per Share											$ 23.30
Share Price											$ 23.29
Stock Issued During Period, Shares, New Issues	3,137,768	3,300,000
Proceeds from Issuance of Common Stock	$ 73,110,000	$ 76,890,000	$ 150,000,000
Common Stock, Shares Authorized				38,838,884		38,838,884	38,838,884		38,838,884
Class of Warrant or Right, Outstanding				784		784
Common Class A [Member] | Shelf Registration [Member]
Sale of Stock, Shelf Registration, Value, Available to Issue										$ 200,000,000
Sale of Stock, Shelf Registration, Value, Incremental Amount Available to Issue										$ 50,000,000
Common Class A [Member] | Shelf Registration [Member] | Cowen and Company LLC [Member]
Stock Issued During Period, Shares, New Issues				589,997		1,789,226
Proceeds from Issuance of Common Stock				$ 14,606,857		$ 41,852,539
Compensation, Percentage of Common Stock Sales										3.00%
Proceeds from Issuance of Common Stock, Net				14,156,342
Payments of Stock Issuance Costs				$ 450,515
Common Class B [Member]
Common Stock, Shares Authorized				1,161,116		1,161,116	1,161,116		1,161,116
Class of Warrant or Right, Outstanding				105,556		105,556
Class of Warrant or Right, Number of Securities Called by Warrants or Rights								784

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- Definition

The percentage amount given to the seller or agent in regards to the sale of common stock they facilitate, measured as a percentage of the common stock sold.

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Number of securities into which the class of warrant or right may be converted. For example, but not limited to, 500,000 warrants may be converted into 1,000,000 shares.

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-SubTopic 10
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The cash outflow for cost incurred directly with the issuance of an equity security.

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The maximum number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) permitted to be issued by an entity's charter and bylaws.

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