Note 4 - Property and Equipment, Net (Details Textual) - USD ($)	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Depreciation, Total	$ 21,000	$ 29,000	$ 196,000	$ 61,000
Laboratory Equipment [Member] \| Research and Development Expense [Member]
Impairment of Long-Lived Assets Held-for-use	$ 0		$ 133,000

The aggregate amount of write-downs for impairments recognized during the period for long lived assets held for use (including those held for disposal by means other than sale).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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