Investments (Narrative) (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Investment [Line Items]
Average remaining maturities for short-term available for sale investments			7 months
Average remaining maturities for long-term available for sale investments			3 years
Proceeds from available-for-sale of investments	$ 606,500,000	$ 143,600,000	$ 872,900,000	$ 375,300,000
Gross unrealized loss on available-for-sale investments	689,000		689,000		635,000
Other Assets [Member]
Investment [Line Items]
Cost method investments	15,200,000		15,200,000		24,300,000
Other Income (Expense) [Member]
Investment [Line Items]
Realized gains on the sales of available-for-sale investments	900,000	100,000	1,200,000	300,000
Realized losses on the sales of available-for-sale investments	200,000	100,000	300,000	200,000
Cost-method investment, gains included in other income	1,500,000
Level 3 [Member] | Fair Value, Measurements, Nonrecurring [Member]
Investment [Line Items]
Cost method investment, impairment charge included other income			3,200,000
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