Note 8 - Unrealized Gains and Losses on Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Money Market Funds [Member]
Adjusted Cost	$ 26,884	$ 31,640
Total Fair Value	26,884	31,640
Certificates of Deposit [Member]
Adjusted Cost	18,607	21,574
Total Fair Value	18,607	21,574
US Government Agencies Short-term Debt Securities [Member]
Adjusted Cost	155,034	123,698
Total Fair Value	155,086	123,532
Unrealized Gains	66	4
Unrealized Losses	(14)	(170)
Fair Value of Investments in Unrealized Loss Position	45,602	110,720
Auction Rate Securities [Member]
Adjusted Cost	5,570	5,570
Total Fair Value	5,353	5,361
Unrealized Losses	(217)	(209)
Fair Value of Investments in Unrealized Loss Position	5,353	5,361
Adjusted Cost	206,095	182,482
Total Fair Value	205,930	182,107
Unrealized Gains	66	4
Unrealized Losses	(231)	(379)
Fair Value of Investments in Unrealized Loss Position	$ 50,955	$ 116,081