Investments (Narrative) (Details) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Investments [Abstract]
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	$ 266,400,000	$ 231,800,000
Realized gains on the sales of available-for-sale investments	300,000	200,000
Realized losses on the sales of available-for-sale investments	100,000	100,000
Gross unrealized loss on available-for-sale investments	746,000		635,000
Cost method investments	18,500,000		24,300,000
Cost method investment, impairment charge included other income	$ 5,200,000