Cash and Cash Equivalents and Investments in Marketable Securities (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 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	$ 0.5	$ 0.3