Note 4 - Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Money market funds	$ 35,775	$ 136,052
Total assets	35,775	136,052
Contingent consideration liability	3,900	11,000
Total liabilities	3,900	11,000
Money market funds	35,775	136,052
Total assets	35,775	136,052
Fair value	3,900	11,000
Total liabilities	3,900	11,000
Fair Value, Inputs, Level 1 [Member]
Money market funds	35,775	136,052
Total assets	35,775	136,052
Contingent consideration liability
Total liabilities
Money market funds	35,775	136,052
Total assets	35,775	136,052
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	3,900	11,000
Total liabilities	3,900	11,000
Money market funds
Total assets
Fair value	3,900	11,000
Total liabilities	$ 3,900	$ 11,000