Investments (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Investment [Line Items]
Average remaining maturities for short-term available for sale investments, in months	6 months
Average remaining maturities for long-term available for sale investments, in years	2 years
Realized gains on the sales of available-for-sale investments	$ 100,000	$ 800,000
Realized losses on the sales of available-for-sale investments	1,500,000	500,000
Other-than-temporary impairment, available-for-sale securities	4,600,000
Gross realized losses on available-for-sale securities not deemed other-than-temporary	2,900,000	7,300,000
Significant Unobservable Inputs (Level 3)
Investment [Line Items]
Adjustments to direct investments in privately-held companies	0
Private Equity Funds
Investment [Line Items]
Alternative Investment	10,900,000
Other Assets
Investment [Line Items]
Direct investments in privately-held companies	$ 13,400,000
Cost method investments		$ 18,600,000