Investments (Details Textual) (USD $) In Millions, unless otherwise specified	9 Months Ended	3 Months Ended					9 Months Ended
	Sep. 30, 2012	Sep. 30, 2012 Auction rate notes [Member]	Sep. 30, 2012 Minimum [Member]	Sep. 30, 2012 Maximum [Member]	Sep. 30, 2012 Maximum [Member] Auction rate notes [Member]	Dec. 31, 2011 Maximum [Member] Auction rate notes [Member]	Sep. 30, 2012 Short-term Investments [Member]	Sep. 30, 2012 Short-term Investments [Member] Minimum [Member]	Sep. 30, 2012 Short-term Investments [Member] Maximum [Member]	Sep. 30, 2012 Long-term Investments [Member]	Sep. 30, 2012 Fair Value Measurements Using Significant Unobservable Inputs (Level 3) [Member]
Investments (Textual) [Abstract]
Maturity period for short-term investments purchased								3 months	12 months
Maturity period for long-term investments purchased										12 months or greater
Unrealized loss on short-term investments							$ 39.9
Temporary impairment of these securities to accumulated other comprehensive income pre tax							0.4
Temporary impairment of these securities to accumulated other comprehensive income Net of tax							0.2
Fair value of auction rate notes											7.7
Period for principal repayments by issuer			20 years	35 years
Maximum interest rate for the auction rate notes' held					1.50%	1.50%
Comprehensive income net of tax due to auction rate notes		0.5
Comprehensive income before tax due to auction rate notes		$ 0.8
Investments (Additional Textual) [Abstract]
Short-term interest rate reset dates of auction rate note securities	less than ninety days
Auction rate note securities with contractual maturities	excess of ten years
Reset period for the securities held	seven or twenty eight days