Note 2 - Investments and Restricted Cash - Current Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Amortized cost	$ 36,546	$ 29,166
Unrealized loss	(41)	(49)
Short-term investments	36,505	29,117
Corporate Bond Securities [Member]
Amortized cost	30,077	22,100
Unrealized loss	(38)	(46)
Short-term investments	30,039	22,054
Municipal Bonds [Member]
Amortized cost	3,138	3,727
Unrealized loss		(1)
Short-term investments	3,138	3,726
US Government Agencies Debt Securities [Member]
Amortized cost	3,331	3,339
Unrealized loss	(3)	(2)
Short-term investments	$ 3,328	$ 3,337