Cash and Cash Equivalents and Investments in Marketable Securities (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Schedule of Available-for-sale Securities [Line Items]
Maximum term to maturity from date of purchase (years)	2 years
Categories of Investments, Marketable Securities, Available-for-sale Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Investment Income, interest income on Marketable Securities	$ 0.6	$ 0.2	$ 1.1	$ 0.5