Consolidated Statements of Stockholders' Equity (Deficit) (Unaudited) (Parentheticals) - shares	3 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020
Common Stock [Member]
Employee stock purchase plan sales, shares (in shares)	123,000		193,000	137,000		110,000
Exercise of stock options, shares (in shares)		1,056,000	593,000		193,000
Issuance of common stock, shares (in shares)					22,044,000
Exercise of stock options, shares (in shares)	942,000
Warrants issued (in shares)					3,511,000