Note 4 - Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Money market funds	$ 20,744	$ 35,775
Total assets	20,744	35,775
Contingent consideration liability	3,600	3,900
Total liabilities	3,600	3,900
Money market funds	20,744	35,775
Total assets	20,744	35,775
Fair value	3,600	3,900
Total liabilities	3,600	3,900
Fair Value, Inputs, Level 1 [Member]
Money market funds	20,744	35,775
Total assets	20,744	35,775
Contingent consideration liability
Total liabilities
Money market funds	20,744	35,775
Total assets	20,744	35,775
Fair value
Total liabilities
Fair Value, Inputs, Level 2 [Member]
Money market funds
Total assets
Contingent consideration liability
Total liabilities
Money market funds
Total assets
Fair value
Total liabilities
Fair Value, Inputs, Level 3 [Member]
Money market funds
Total assets
Contingent consideration liability	3,600	3,900
Total liabilities	3,600	3,900
Money market funds
Total assets
Fair value	3,600	3,900
Total liabilities	$ 3,600	$ 3,900