Note 10- Cash, Cash Equivalents, Investments and Restricted Cash - Unrealized Gains and Losses on Investments (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Adjusted Cost	$ 214,742	$ 250,800
Unrealized Gains	244	9
Unrealized Losses	(492)	(1,856)
Total Fair Value	214,494	248,953
Fair Value of Investments in Unrealized Loss Position	86,051	197,952
Money Market Funds [Member]
Adjusted Cost	41,820	41,135
Unrealized Gains	0	0
Unrealized Losses	0	0
Total Fair Value	41,820	41,135
Fair Value of Investments in Unrealized Loss Position	0	0
Corporate Debt Securities [Member]
Adjusted Cost	135,520	172,288
Unrealized Gains	224	7
Unrealized Losses	(196)	(1,386)
Total Fair Value	135,548	170,909
Fair Value of Investments in Unrealized Loss Position	67,113	166,204
US Government Agencies Short-term Debt Securities [Member]
Adjusted Cost	32,307	32,207
Unrealized Gains	20	2
Unrealized Losses	(16)	(141)
Total Fair Value	32,311	32,068
Fair Value of Investments in Unrealized Loss Position	15,723	28,507
Certificates of Deposit [Member]
Adjusted Cost	1,600	1,600
Unrealized Gains	0	0
Unrealized Losses	0	0
Total Fair Value	1,600	1,600
Fair Value of Investments in Unrealized Loss Position	0	0
Auction Rate Securities [Member]
Adjusted Cost	3,495	3,570
Unrealized Gains	0	0
Unrealized Losses	(280)	(329)
Total Fair Value	3,215	3,241
Fair Value of Investments in Unrealized Loss Position	$ 3,215	$ 3,241