Note 6 - Marketable Securities - Short-term and Long-term Marketable Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
US States and Political Subdivisions Debt Securities [Member]
Amortized Cost	$ 42,718	$ 35,667
Unrealized Gains	7	8
Unrealized Losses	(76)	(56)
Fair Value	42,649	35,619
Corporate Debt Securities [Member]
Amortized Cost	32,745	28,133
Unrealized Gains	18
Unrealized Losses	(33)	(114)
Fair Value	32,730	28,019
US Government Agencies Debt Securities [Member]
Amortized Cost	24,770	26,784
Unrealized Gains	4	2
Unrealized Losses	(25)	(99)
Fair Value	24,749	26,687
Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Amortized Cost		1,497
Unrealized Gains
Unrealized Losses		(2)
Fair Value		1,495
Bank Time Deposits [Member]
Amortized Cost	7,182	5,909
Unrealized Gains	32	2
Unrealized Losses		(11)
Fair Value	7,214	5,900
Amortized Cost	107,415	97,990
Unrealized Gains	61	12
Unrealized Losses	(134)	(282)
Fair Value	$ 107,342	$ 97,720