Marketable Securities and Investments (Narrative) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2011 years countries customers	Dec. 31, 2010 years customers
Schedule of Available-for-sale Securities [Line Items]
Cash flow analysis weighted average discount rate	4.11%	3.21%
Cash flow analysis expected term (in years)	5	5
Estimated aggregate loss related to impairment of auction rate securities included in accumulated other comprehensive income loss	$ 16.6	$ 13.5
Auction rate securities classified as long term marketable securities on balance sheet	118.8	137.3
Auction Rate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost of auction rate securities	$ 135.4