Note 3 - Fair Value Measurements - Fair Value of Assets Measured on a Recurring Basis (Details) - Fair Value, Recurring [Member] - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Cash and Cash Equivalents, Fair Value	$ 21,407	$ 5,585
Money Market Funds [Member]
Cash and Cash Equivalents, Fair Value	20,662	4,637
Demand Deposits [Member]
Cash and Cash Equivalents, Fair Value	745	948
Fair Value, Inputs, Level 1 [Member]
Cash and Cash Equivalents, Fair Value	20,662	4,637
Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Cash and Cash Equivalents, Fair Value	20,662	4,637
Fair Value, Inputs, Level 1 [Member] | Demand Deposits [Member]
Cash and Cash Equivalents, Fair Value
Fair Value, Inputs, Level 2 [Member]
Cash and Cash Equivalents, Fair Value
Fair Value, Inputs, Level 2 [Member] | Money Market Funds [Member]
Cash and Cash Equivalents, Fair Value
Fair Value, Inputs, Level 2 [Member] | Demand Deposits [Member]
Cash and Cash Equivalents, Fair Value
Fair Value, Inputs, Level 3 [Member]
Cash and Cash Equivalents, Fair Value
Fair Value, Inputs, Level 3 [Member] | Money Market Funds [Member]
Cash and Cash Equivalents, Fair Value
Fair Value, Inputs, Level 3 [Member] | Demand Deposits [Member]
Cash and Cash Equivalents, Fair Value