Note 8 - Cash Equivalents, Short-term and Long-term Investments (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Dec. 31, 2014
Corporate Debt Securities [Member]
Available-for-sale securities	$ 7,581
Auction Rate Securities [Member]
Available-for-sale securities	5,294	5,361
Cash	54,182	58,217
Money market funds	27,864	31,640
Certificates of deposit	7,525	21,574
U.S. treasuries and government agency bonds	146,712	123,532
Total	249,158	240,324
Cash and cash equivalents	82,046	90,860	$ 80,868	$ 126,266
Short-term investments	161,818	144,103
Long-term investments	$ 5,294	$ 5,361