Long-Term Debt (Details Textual) (USD $) In Millions, unless otherwise specified						9 Months Ended		1 Months Ended			9 Months Ended
	Sep. 30, 2012	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2012 7.125 Percent Notes Due May 2016 [Member]	Apr. 28, 2006 7.125 Percent Notes Due May 2016 [Member]	Sep. 30, 2012 5.375 Percent Notes [Member]	Oct. 03, 2012 5.375 Percent Notes [Member]	Apr. 30, 2006 7 1/8% Notes, due May 2016-net of original issue discount [Member]	Sep. 30, 2012 Letter of Credit [Member]	Dec. 31, 2011 Letter of Credit [Member]	Sep. 30, 2012 Revolving Credit Facility [Member]	Nov. 21, 2011 Revolving Credit Facility [Member]	Sep. 30, 2012 Maximum [Member] Revolving Credit Facility [Member]	Sep. 30, 2012 Minimum [Member] Revolving Credit Facility [Member]
Long- Term Debt (Textual) [Abstract]
Line of credit facility, maximum borrowing capacity												$ 350
Debt instrument maturity date						Oct. 03, 2020					Nov. 21, 2016
Federal fund rate Spread													1.25%	0.25%
Spread, Euro-rate													2.25%	1.25%
Outstanding Amount of Debt					200.0		250.0
Proceeds from note offering, net of original issue discount						246.3		196.4
Letter of credit outstanding									$ 5.2	$ 4.6
Percentage of aggregate principal amount of outstanding	7.125%	7.125%	7.125%	7.125%		5.375%	5.375%
Long Term Debt (Additional Textual) [Abstract]
Margin over federal fund rate	0.50%	0.50%
Margin over Euro-rate	1.00%	1.00%