Note 2 - Investments - Current Investments (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Amortized cost	$ 37,849	$ 29,166
Unrealized loss	(33)	(49)
Fair market value	37,816	29,117
Corporate Bond Securities [Member]
Amortized cost	34,533	22,100
Unrealized loss	(33)	(46)
Fair market value	34,500	22,054
Municipal Bonds [Member]
Amortized cost	1,715	3,727
Unrealized loss		(1)
Fair market value	1,715	3,726
US Government Agencies Debt Securities [Member]
Amortized cost	1,601	3,339
Unrealized loss		(2)
Fair market value	$ 1,601	$ 3,337