Investments (Narrative) (Details) (USD $)	3 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2012	Dec. 31, 2011
Investments [Abstract]
Average remaining maturities for short-term available for sale investments, in months		5 months
Average remaining maturities for long-term available for sale investments, in years		4 years
Realized gains on the sales of available-for-sale investments		$ 4,100,000	$ 400,000
Realized losses on the sales of available-for-sale investments		800,000	1,800,000
Available-for-sale securities, carrying value	5,000,000	876,988,000	1,140,422,000
Available-for-sale securities, fair value	2,500,000	880,335,000	1,144,305,000
Other than temporary charge included in income	2,500,000
Gross unrealized losses		192,000	1,504,000
Cost method investments		26,200,000	32,200,000
Cost method investments, gain recorded on cost method investments		16,500,000
Cost method investment, impairment charge included other income		$ 3,500,000	$ 3,500,000