Note 6 - Marketable Securities - Balance of Held-to-Maturity Debt Securities by Contractual Maturity (Details) - USD ($)
$ in Thousands
Sep. 30, 2016
Dec. 31, 2015
Due in one year or less $ 39,028  
Due after one year through five years 68,387  
Total marketable securities $ 107,415 $ 97,990