Note 7 - Short-term and Long-term Marketable Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
US Government Agencies Debt Securities [Member]
Amortized Cost	$ 26,784	$ 20,048
Unrealized Gains	2
Unrealized Losses	(99)	$ (71)
Fair Value	26,687	19,977
Corporate Debt Securities [Member]
Amortized Cost	$ 28,133	29,316
Unrealized Gains		7
Unrealized Losses	$ (114)	(79)
Fair Value	28,019	29,244
Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Amortized Cost	$ 1,497
Unrealized Gains
Unrealized Losses	$ (2)
Fair Value	1,495
US States and Political Subdivisions Debt Securities [Member]
Amortized Cost	35,667	30,004
Unrealized Gains	8	32
Unrealized Losses	(56)	(18)
Fair Value	35,619	30,018
Bank Time Deposits [Member]
Amortized Cost	5,909	5,656
Unrealized Gains	2	5
Unrealized Losses	(11)	(15)
Fair Value	5,900	5,646
Amortized Cost	97,990	85,024
Unrealized Gains	12	44
Unrealized Losses	(282)	(183)
Fair Value	$ 97,720	$ 84,885