Note 8 - Cash Equivalents, Short-term and Long-term Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Auction Rate Securities [Member]
Cash, cash equivalents and investments:
Auction-rate securities backed by student-loan notes	$ 5,353	$ 5,361
Cash	50,924	58,217
Money market funds	26,884	31,640
Certificates of deposit	18,607	21,574
U.S. treasuries and government agency bonds	155,086	123,532
Total	256,854	240,324
Cash and cash equivalents	77,808	90,860	$ 95,966	$ 126,266
Short-term investments	173,693	144,103
Long-term investments	$ 5,353	$ 5,361