Summary of Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 year month	Dec. 31, 2011	Dec. 31, 2012 Customer concentration Accounts receivable	Dec. 31, 2011 Customer concentration Accounts receivable	Dec. 31, 2012 Customer concentration Revenues.	Dec. 31, 2011 Customer concentration Revenues.	Dec. 31, 2010 Customer concentration Revenues.
Cash and Cash Equivalents
Maximum original term of maturities of cash and cash equivalents (in months)	3
Maximum term of maturities of time deposits (in months)	3
Restricted Cash
Maximum period until release for current restricted cash (in years)	1
Restricted Cash	$ 7.6	$ 6.1
Restricted Cash, non current	3.9	3.9
Concentration of Credit Risk
Allowance for doubtful accounts	$ 7.9	$ 5.6
Threshold for disclosure of risk concentrations (as a percent)			10.00%	10.00%	10.00%	10.00%	10.00%