Note 9 - Fair Value Measurements - Financial Assets and Liabilities, Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Total Fair Value	$ 47,261	$ 31,640
Money Market Funds [Member]
Total Fair Value	47,261	31,640
Certificates of Deposit [Member] | Fair Value, Inputs, Level 2 [Member]
Total Fair Value	7,495	21,574
Certificates of Deposit [Member]
Total Fair Value	7,495	21,574
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Total Fair Value	20,665
Corporate Debt Securities [Member]
Total Fair Value	20,665
US Government Agencies Short-term Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Total Fair Value	121,424	123,532
US Government Agencies Short-term Debt Securities [Member]
Total Fair Value	121,424	123,532
Auction Rate Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Total Fair Value	5,382	5,361
Auction Rate Securities [Member]
Total Fair Value	5,382	5,361
Mutual Fund [Member] | Fair Value, Inputs, Level 1 [Member]
Total Fair Value	9,304	8,279
Mutual Fund [Member]
Total Fair Value	9,304	8,279
Fair Value, Inputs, Level 1 [Member]
Total Fair Value	56,565	39,919
Fair Value, Inputs, Level 2 [Member]
Total Fair Value	149,584	145,106
Fair Value, Inputs, Level 3 [Member]
Total Fair Value	5,382	5,361
Total Fair Value	202,227	182,107
Total Fair Value	$ 211,531	$ 190,386