Investments (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Investment [Line Items]
Average remaining maturities for short-term available for sale investments			8 months
Average remaining maturities for long-term available for sale investments			3 years
Proceeds from available-for-sale of investments	$ 709,200,000	$ 718,400,000	$ 1,160,000,000	$ 1,550,000,000
Gross unrealized losses on available-for-sale investments	661,000		661,000		$ 3,493,000
Other Assets [Member]
Investment [Line Items]
Cost method investments	19,700,000		19,700,000		$ 19,900,000
Other Income (Expense) [Member]
Investment [Line Items]
Realized gains on the sales of available-for-sale investments	1,000,000	300,000	1,600,000	700,000
Realized losses on the sales of available-for-sale investments	100,000	600,000	300,000	900,000
Level 3 [Member] | Fair Value, Measurements, Nonrecurring [Member]
Investment [Line Items]
Cost-method investments, aggregate carrying amount, evaluated for impairment during the period	1,000,000		1,200,000
Cost method investments, fair value after impairment	100,000		100,000
Level 3 [Member] | Fair Value, Measurements, Nonrecurring [Member] | Other Income (Expense) [Member]
Investment [Line Items]
Impairment of intangible assets	$ 900,000	0	$ 1,100,000
Cost method investment, impairment charge included other income		$ 0		$ 3,000,000