Note 6 - Fair Value Measurements - Fair Value of Financial Assets Measured on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Marketable securities	$ 36,099
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Cash and cash equivalents	47,337	$ 72,225
Marketable securities	11,872	0
Total	59,674	127,603
Contingent consideration	0	0
Total	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Cash and cash equivalents	465	55,378
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Cash and cash equivalents	0	0
Marketable securities	24,227	0
Total	24,227	0
Contingent consideration	0	0
Total	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Money Market Funds [Member]
Cash and cash equivalents	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Cash and cash equivalents	0	0
Marketable securities	0	0
Total	0	0
Contingent consideration	4,800	0
Total	4,800	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Money Market Funds [Member]
Cash and cash equivalents	$ 0	$ 0