Note 2 - Summary of Significant Accounting Policies (Details Textual) $ in Thousands	3 Months Ended
Mar. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Retained Earnings (Accumulated Deficit), Total	$ (552,862)	$ (539,805)
Working Capital (Deficit)	49,300
Cash and Cash Equivalents, at Carrying Value, Total	$ 65,825	$ 59,424
Number of Operating Segments	1
Minimum [Member]
Property, Plant and Equipment, Useful Life (Year)	3 years
Maximum [Member]
Property, Plant and Equipment, Useful Life (Year)	5 years

Represents the value of total current assets net of current liabilities as of the balance sheet date.

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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

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The cumulative amount of the reporting entity's undistributed earnings or deficit.

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