Investments (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Investments, Debt and Equity Securities [Abstract]
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	3 years
Realized gains on the sales of available-for-sale investments	$ 1,900,000	$ 3,000,000
Realized losses on the sales of available-for-sale investments	500,000	2,700,000
Available-for-sale investments, carrying value	1,602,904,000	1,307,910,000
Available-for-sale investments, fair value	1,602,370,000	1,309,676,000
Gross unrealized losses	2,116,000	635,000
Cost method investments	16,600,000	24,300,000
Cost method investments, gain recorded on cost method investments	2,900,000	6,000,000
Cost method investment, impairment charge included other income	$ 8,300,000	$ 3,700,000	$ 3,500,000