Balance Sheet Components (Schedule Of Available-For-Sale Short-Term) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 124,978	$ 124,017
Unrealized Gain	0	9
Unrealized Loss	(146)	(40)
Estimated Fair Value	124,832	123,986
Treasuries [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	124,816	123,869
Unrealized Gain	0	9
Unrealized Loss	(146)	(40)
Estimated Fair Value	124,670	123,838
Certificates Of Deposits [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	162	148
Unrealized Gain	0	0
Unrealized Loss	0	0
Estimated Fair Value	$ 162	$ 148