Note 9 - Financial Assets and Liabilities, Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Assets	$ 26,884	$ 31,640
Money Market Funds [Member]
Assets	26,884	31,640
Certificates of Deposit [Member] | Fair Value, Inputs, Level 2 [Member]
Assets	18,607	21,574
Certificates of Deposit [Member]
Assets	18,607	21,574
US Government Agencies Short-term Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Assets	155,086	123,532
US Government Agencies Short-term Debt Securities [Member]
Assets	155,086	123,532
Auction Rate Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Assets	5,353	5,361
Auction Rate Securities [Member]
Assets	5,353	5,361
Mutual Fund under Deferred Compensation Plan [Member] | Fair Value, Inputs, Level 1 [Member]
Assets	9,505	8,279
Mutual Fund under Deferred Compensation Plan [Member]
Assets	9,505	8,279
Fair Value, Inputs, Level 1 [Member]
Assets	36,389	39,919
Fair Value, Inputs, Level 2 [Member]
Assets	173,693	145,106
Fair Value, Inputs, Level 3 [Member]
Assets	5,353	5,361
Assets	$ 215,435	$ 190,386