Note 10- Cash, Cash Equivalents, Investments and Restricted Cash - Unrealized Gains and Losses on Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Adjusted Cost	$ 259,239	$ 250,800
Total Fair Value	259,263	248,953
Unrealized Gains	335	9
Unrealized Losses	(311)	(1,856)
Fair Value of Investments in Unrealized Loss Position	94,509	197,952
Money Market Funds [Member]
Adjusted Cost	39,982	41,135
Total Fair Value	39,982	41,135
Corporate Debt Securities [Member]
Adjusted Cost	195,471	172,288
Total Fair Value	195,667	170,909
Unrealized Gains	324	7
Unrealized Losses	(128)	(1,386)
Fair Value of Investments in Unrealized Loss Position	83,247	166,204
US Government Agencies Short-term Debt Securities [Member]
Adjusted Cost	20,341	32,207
Total Fair Value	20,350	32,068
Unrealized Gains	11	2
Unrealized Losses	(2)	(141)
Fair Value of Investments in Unrealized Loss Position	7,998	28,507
Auction Rate Securities [Member]
Adjusted Cost	3,445	3,570
Total Fair Value	3,264	3,241
Unrealized Losses	(181)	(329)
Fair Value of Investments in Unrealized Loss Position	$ 3,264	3,241
Certificates of Deposit [Member]
Adjusted Cost		1,600
Total Fair Value		$ 1,600