Note 4 - Stockholders' Equity - Stock Options by Exercise Price Range (Details) - USD ($)	9 Months Ended	12 Months Ended
Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Number of options outstanding (in shares)	1,800,922	271,660
Weighted- average exercise price (in dollars per share)	$ 8.55	$ 61.83	$ 215.60
Weighted- average remaining contractual life (Year)	9 years 109 days	7 years 292 days	5 years 36 days
Aggregate intrinsic value
Range One [Member]
Range of exercise prices, lower limit (in dollars per share)	$ 0.62	$ 5.90
Range of exercise prices, upper limit (in dollars per share)	$ 0.62	$ 6
Number of options outstanding (in shares)	1,686,466	55,484
Weighted- average exercise price (in dollars per share)	$ 0.62	$ 5.99
Weighted- average remaining contractual life (Year)	9 years 182 days	9 years 182 days
Aggregate intrinsic value
Range Two [Member]
Range of exercise prices, lower limit (in dollars per share)	$ 5.90	$ 7.20
Range of exercise prices, upper limit (in dollars per share)	$ 6	$ 8.80
Number of options outstanding (in shares)	45,378	146,972
Weighted- average exercise price (in dollars per share)	$ 5.99	$ 8.51
Weighted- average remaining contractual life (Year)	8 years 292 days	9 years
Aggregate intrinsic value
Range Three [Member]
Range of exercise prices, lower limit (in dollars per share)	$ 7.20	$ 22.20
Range of exercise prices, upper limit (in dollars per share)	$ 8.80	$ 99.20
Number of options outstanding (in shares)	6,380	28,501
Weighted- average exercise price (in dollars per share)	$ 8.69	$ 31.63
Weighted- average remaining contractual life (Year)	8 years 146 days	5 years 255 days
Aggregate intrinsic value
Range Four [Member]
Range of exercise prices, lower limit (in dollars per share)	$ 22.20	$ 107.40
Range of exercise prices, upper limit (in dollars per share)	$ 80.60	$ 1,102.41
Number of options outstanding (in shares)	24,488	40,703
Weighted- average exercise price (in dollars per share)	$ 31.15	$ 351.63
Weighted- average remaining contractual life (Year)	4 years 292 days	2 years 292 days
Aggregate intrinsic value

Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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The floor of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

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The number of shares reserved for issuance pertaining to the outstanding stock options as of the balance sheet date for all option plans in the customized range of exercise prices.

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The ceiling of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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