Note 10 - Net Loss Per Share Attributable to Common Stockholders (Details Textual) - $ / shares shares in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2015
Securities Excluded from Computation of Earnings Per Share Amount, Performance Conditions	3.6	10.8
Sale of Stock, Price Per Share			$ 17.50
Number of Trading Days of Share Price			20 days
Total Number of Trading Days Considered			30 days
IPO Warrants [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights			$ 11.50
Class of Warrant or Right, Redemption Price of Warrant or Right			$ 0.01
Class of Warrant or Right, Number of Days Notice to Redeem			30 days