Note 4 - Property and Equipment, Net (Details Textual) - USD ($)	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Depreciation, Total	$ 174,000	$ 32,000
Laboratory Equipment [Member] \| Research and Development Expense [Member]
Impairment of Long-Lived Assets Held-for-use	$ 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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-Name Accounting Standards Codification
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 2
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-URI http://asc.fasb.org/extlink&oid=109226691&loc=d3e2921-110230

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 958
-SubTopic 220
-Section 45
-Paragraph 11
-Subparagraph (a)
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
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Period Type:	duration