Note 3 - Marketable Securities and Time Deposits - Marketable Securities and Time Deposits (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Available-for-sale Securities, Amortized Cost Basis, Total	$ 112,885	$ 108,575
Marketable securities and time deposits, unrealized gains (losses), net	(1,635)	(1,209)
Available-for-sale Securities, Total	111,251	107,366
Short-term Deposits [Member]
Available-for-sale Securities, Amortized Cost Basis, Total	8,349	5,481
Marketable securities and time deposits, unrealized gains (losses), net
Available-for-sale Securities, Total	8,349	5,481
Long-Term Deposit [Member]
Available-for-sale Securities, Amortized Cost Basis, Total	5,130	5,013
Marketable securities and time deposits, unrealized gains (losses), net
Available-for-sale Securities, Total	5,130	5,013
US Government-sponsored Enterprises Debt Securities [Member]
Available-for-sale Securities, Amortized Cost Basis, Total	21,550	22,359
Marketable securities and time deposits, unrealized gains (losses), net	(253)	(315)
Available-for-sale Securities, Total	21,297	22,044
Corporate Debt Securities [Member]
Available-for-sale Securities, Amortized Cost Basis, Total	77,857	75,722
Marketable securities and time deposits, unrealized gains (losses), net	(1,382)	(894)
Available-for-sale Securities, Total	$ 76,475	$ 74,828