Note 3 - Marketable Securities and Time Deposits - Marketable Securities and Time Deposits (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale, Amortized Cost, Total	$ 87,024	$ 99,406
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax, Total	66
Debt Securities, Available-for-sale, Total	86,958	97,772
Debt Securities and Time Deposits [Member]
Debt Securities, Available-for-sale, Amortized Cost, Total	102,091	112,885
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax, Total	(66)	(1,635)
Debt Securities, Available-for-sale, Total	102,025	111,251
Short-term Deposits [Member] | Debt Securities and Time Deposits [Member]
Debt Securities, Available-for-sale, Amortized Cost, Total	15,067	8,349
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax, Total
Debt Securities, Available-for-sale, Total	15,067	8,349
Long-Term Deposit [Member] | Debt Securities and Time Deposits [Member]
Debt Securities, Available-for-sale, Amortized Cost, Total		5,130
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax, Total
Debt Securities, Available-for-sale, Total		5,130
US Government-sponsored Enterprises Debt Securities [Member] | Debt Securities and Time Deposits [Member]
Debt Securities, Available-for-sale, Amortized Cost, Total	4,468	21,550
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax, Total	(6)	(253)
Debt Securities, Available-for-sale, Total	4,462	21,297
Corporate Debt Securities [Member] | Debt Securities and Time Deposits [Member]
Debt Securities, Available-for-sale, Amortized Cost, Total	82,556	77,857
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax, Total	(60)	(1,382)
Debt Securities, Available-for-sale, Total	$ 82,496	$ 76,475