Note 9 - Fair Value Measurements - Financial Assets and Liabilities, Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Total Fair Value	$ 235,092	$ 197,939
Total Fair Value	220,853	185,831
Fair Value, Inputs, Level 1 [Member]
Total Fair Value	23,183	37,064
Fair Value, Inputs, Level 2 [Member]
Total Fair Value	206,561	155,521
Fair Value, Inputs, Level 3 [Member]
Total Fair Value	5,348	5,354
Money Market Funds [Member]
Total Fair Value	8,944	24,956
Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Total Fair Value	8,944	24,956
Certificates of Deposit [Member]
Total Fair Value	7,378
Corporate Debt Securities [Member]
Total Fair Value	181,269	109,644
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Total Fair Value	181,269	109,644
US Government Agencies Short-term Debt Securities [Member]
Total Fair Value	17,914	45,877
US Government Agencies Short-term Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Total Fair Value	17,914	45,877
Auction Rate Securities [Member]
Total Fair Value	5,348	5,354
Auction Rate Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Total Fair Value	5,348	5,354
Mutual Fund [Member]
Total Fair Value	14,239	12,108
Mutual Fund [Member] | Fair Value, Inputs, Level 1 [Member]
Total Fair Value	$ 14,239	$ 12,108