Note 2 - Significant Accounting Policies - Summary of Cash Equivalents and Short-term Investment (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Cash and cash equivalents	$ 63,131	$ 85,293
Unrealized gains	0	0
Unrealized losses	(2)	0
Totals, amortized cost	69,849	79,813
Totals, fair value	69,847	79,813
Commercial Paper [Member]
Investments, amortized cost	14,590
Unrealized gains	0
Unrealized losses	(1)
Investments, fair value	14,589
Corporate Bond Securities [Member]
Investments, amortized cost	4,387	8,096
Unrealized gains		0
Unrealized losses	(1)	0
Investments, fair value	4,386	8,096
Cash Equivalents [Member]
Cash and cash equivalents	$ 50,872	$ 71,717

Represents fair value of cash, cash equivalents and short-term investments.

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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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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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Cash includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the customer may deposit additional funds at any time and effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid Investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months. Short-term investments, exclusive of cash equivalents, generally consist of marketable securities intended to be sold within one year (or the normal operating cycle if longer) and may include trading securities, available-for-sale securities, or held-to-maturity securities (if maturing within one year), as applicable.

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