Consolidated Statements of Stockholders' Equity (Parentheticals) - shares shares in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Common Stock [Member]
Exercise of stock options, shares (in shares)	283	1,106	609
Employee stock purchase plan sales, shares (in shares)	115	92	95
Issuance of common stock, shares (in shares)	43,621	10,455	23,925
Warrants issued (in shares)	11,765

Number of share options (or share units) exercised during the current period.

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