Note 2 - Fair Value Measurement - Financial Assets on Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Inputs, Level 2 [Member]
Total cash and cash equivalents	$ 0	$ 0
Fair Value, Recurring [Member]
Total cash and cash equivalents	31,824	30,657
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Total cash and cash equivalents	31,824	30,657
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Total cash and cash equivalents