Note 5 - Supplemental Balance Sheet Information - Amortization of Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Amortization of intangible assets	$ 146	$ 132	$ 295	$ 224
Research and Development Expense [Member]
Amortization of intangible assets	30	33	61	66
Selling, General and Administrative Expenses [Member]
Amortization of intangible assets	$ 116	$ 99	$ 234	$ 158

The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
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-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
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-Section 45
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-URI http://asc.fasb.org/extlink&oid=6388964&loc=d3e16225-109274

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