Marketable Securities and Investments (Narrative) (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2011 customers countries years	Dec. 31, 2010 customers years
Schedule of Available-for-sale Securities [Line Items]
Cash flow analysis weighted average discount rate	2.97%	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	$ 12.2	$ 13.5
Auction rate securities classified as long term marketable securities on balance sheet	124.1	137.3
Auction Rate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost of auction rate securities	$ 136.4