Note 9 - Fair Value Measurements - Financial Assets and Liabilities, Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Total Fair Value	$ 215,431	$ 185,831
Total Fair Value	228,945	197,939
Fair Value, Inputs, Level 1 [Member]
Total Fair Value	21,788	37,064
Fair Value, Inputs, Level 2 [Member]
Total Fair Value	201,815	155,521
Fair Value, Inputs, Level 3 [Member]
Total Fair Value	5,342	5,354
Money Market Funds [Member]
Total Fair Value	8,274	24,956
Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Total Fair Value	8,274	24,956
Certificates of Deposit [Member]
Total Fair Value	7,256
Corporate Debt Securities [Member]
Total Fair Value	170,389	109,644
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Total Fair Value	170,389	109,644
US Government Agencies Short-term Debt Securities [Member]
Total Fair Value	24,170	45,877
US Government Agencies Short-term Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Total Fair Value	24,170	45,877
Auction Rate Securities [Member]
Total Fair Value	5,342	5,354
Auction Rate Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Total Fair Value	5,342	5,354
Mutual Fund [Member]
Total Fair Value	13,514	12,108
Mutual Fund [Member] | Fair Value, Inputs, Level 1 [Member]
Total Fair Value	$ 13,514	$ 12,108