Note 3 - Cash, Cash Equivalents and Investments (Details) - Cash Equivalents, Short-term and Long-term Investments - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash, cash equivalents and investments:
Cash	$ 58,217	$ 66,188
Money market funds	31,640	60,078
Certificates of deposit	21,574	22,778
U.S. treasuries and government agency bonds	123,532	89,674
Total	240,324	244,107
Cash and cash equivalents	90,860	126,266	$ 101,213	$ 75,104
Short-term investments	144,103	112,452
Long-term investments	5,361	5,389
Auction Rate Securities [Member]
Cash, cash equivalents and investments:
Auction-rate securities backed by student-loan notes	$ 5,361	$ 5,389