Note 10 - Net Loss Per Share - Anti-dilutive Securities (Details) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Anti-dilutive securities (in shares)	1,584	1,972	1,328	1,719
Share-based Payment Arrangement, Option [Member]
Anti-dilutive securities (in shares)	310	525	362	584
Restricted Stock Units (RSUs) [Member]
Anti-dilutive securities (in shares)	1,084	1,394	820	985
Employee Stock Purchase Plan [Member]
Anti-dilutive securities (in shares)	190	53	146	150