Note 5 - Fair Value Measurements - Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands |
Jun. 30, 2018 |
Dec. 31, 2017 |
---|---|---|
Cash equivalents | $ 60,962 | $ 6,393 |
Investments | 13,250 | 24,000 |
Fair Value, Inputs, Level 1 [Member] | ||
Cash equivalents | 60,962 | 5,893 |
Fair Value, Inputs, Level 2 [Member] | ||
Cash equivalents | 500 | |
Money Market Funds [Member] | ||
Cash equivalents | 17,366 | 5,893 |
Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member] | ||
Cash equivalents | 17,366 | 5,893 |
US Treasury Securities [Member] | ||
Cash equivalents | 43,596 | |
US Treasury Securities [Member] | Fair Value, Inputs, Level 1 [Member] | ||
Cash equivalents | 43,596 | |
Certificates of Deposit [Member] | ||
Cash equivalents | 500 | |
Investments | 13,250 | 24,000 |
Certificates of Deposit [Member] | Fair Value, Inputs, Level 2 [Member] | ||
Cash equivalents | 500 | |
Investments | $ 13,250 | $ 24,000 |