Investments (Narrative) (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Investment [Line Items]
Average remaining maturities for short-term available for sale investments			6 months
Average remaining maturities for long-term available for sale investments			3 years
Proceeds from available-for-sale of investments	$ 469,600,000	$ 111,500,000	$ 1,342,500,000	$ 486,800,000
Gross unrealized loss on available-for-sale investments	1,402,000		1,402,000		635,000
Other Assets [Member]
Investment [Line Items]
Cost method investments	16,200,000		16,200,000		24,300,000
Other Income (Expense) [Member]
Investment [Line Items]
Realized gains on the sales of available-for-sale investments	200,000	100,000	1,400,000	500,000
Realized losses on the sales of available-for-sale investments	100,000	100,000	400,000	400,000
Cost-method investment, gains included in other income	1,200,000		2,700,000
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