Investments (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Investment [Line Items]
Proceeds from available-for-sale of investments	$ 718,400,000	$ 469,600,000	$ 1,550,000,000	$ 1,340,000,000
Average remaining maturities for short-term available for sale investments			6 months
Average remaining maturities for long-term available for sale investments			3 years
Gross unrealized losses on available-for-sale investments	1,009,000		$ 1,009,000		$ 2,116,000
Cost method investments, gain recorded on cost method investments	0		0
Other Assets [Member]
Investment [Line Items]
Cost method investments	17,200,000		17,200,000		$ 16,600,000
Other Income (Expense) [Member]
Investment [Line Items]
Realized gains on the sales of available-for-sale investments	300,000	200,000	700,000	1,400,000
Realized losses on the sales of available-for-sale investments	$ 600,000	100,000	900,000	400,000
Level 3 [Member] | Fair Value, Measurements, Nonrecurring [Member] | Other Income (Expense) [Member]
Investment [Line Items]
Cost method investment, impairment charge included other income		3,200,000	$ 3,000,000	8,300,000
Cost method investments, gain recorded on cost method investments		$ 1,200,000		$ 2,700,000