Note 10- Cash, Cash Equivalents, Investments and Restricted Cash - Unrealized Gains and Losses on Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Adjusted Cost	$ 237,550	$ 250,800
Total Fair Value	236,627	248,953
Unrealized Gains	54	9
Unrealized Losses	(977)	(1,856)
Fair Value of Investments in Unrealized Loss Position	149,997	197,952
Money Market Funds [Member]
Adjusted Cost	56,082	41,135
Total Fair Value	56,082	41,135
Corporate Debt Securities [Member]
Adjusted Cost	144,041	172,288
Total Fair Value	143,453	170,909
Unrealized Gains	44	7
Unrealized Losses	(632)	(1,386)
Fair Value of Investments in Unrealized Loss Position	123,828	166,204
US Government Agencies Short-term Debt Securities [Member]
Adjusted Cost	32,257	32,207
Total Fair Value	32,202	32,068
Unrealized Gains	10	2
Unrealized Losses	(65)	(141)
Fair Value of Investments in Unrealized Loss Position	22,879	28,507
Certificates of Deposit [Member]
Adjusted Cost	1,600	1,600
Total Fair Value	1,600	1,600
Auction Rate Securities [Member]
Adjusted Cost	3,570	3,570
Total Fair Value	3,290	3,241
Unrealized Losses	(280)	(329)
Fair Value of Investments in Unrealized Loss Position	$ 3,290	$ 3,241