Note 6 - Commitments and Contingencies (Details Textual)	3 Months Ended		9 Months Ended	21 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jun. 30, 2015 ft²
Operating Lease, Expense	$ 500,000	$ 500,000	$ 1,400,000	$ 1,400,000
Headquarters and Laboratory Facilities in South San Francisco, California [Member]
Area of Real Estate Property (Square Foot) | ft²						59,000
Headquarters and Laboratory Facilities in South San Francisco, California [Member] | Other Noncurrent Assets [Member]
Security Deposit	603,000			603,000	$ 603,000
Laboratory and Office Space in Austin, Texas [Member] | Other Noncurrent Assets [Member]
Security Deposit	$ 139,000			$ 139,000	$ 139,000