Balance Sheet Components (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Balance Sheet Components [Line Items]
Cost Method Investments	$ 4,500,000	$ 100,000
Cost-method Investments, Other than Temporary Impairment	0	0	$ 0
Amortization expense	12,900,000	17,000,000	17,300,000
Impairment of Intangible Assets (Excluding Goodwill)	0	0	0
Goodwill impairment charges	0	0	$ 0
Goodwill, Impaired, Accumulated Impairment Loss	$ 74,200,000	$ 74,200,000