Investments (Narrative) (Details) (USD $)	3 Months Ended
	Mar. 31, 2012 M Y	Mar. 31, 2011	Dec. 31, 2011
Proceeds from available-for-sale of investments	$ 104,200,000	$ 180,400,000
Realized gains on the sales of available-for-sale investments		200,000
Realized losses on the sales of available-for-sale investments	200,000	600,000
Gross unrealized losses	(741,000)		(1,504,000)
Average remaining maturities for short-term available for sale investments, in months	5
Average remaining maturities for long-term available for sale investments, in years	8
Cost method investments	$ 30,800,000		$ 32,200,000