Derivative Contracts (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013		Dec. 31, 2013
Derivative [Line Items]
Maximum Forecasted Production Covered By Derivatives					100.00%
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	$ 0	[1]	$ 20.6	[1]	$ 0	[1]	$ 40.7	[1]
Long-term Debt, Gross	3,914.8				3,914.8				3,001.8
Term Loan due 2017 [Member]
Derivative [Line Items]
Long-term Debt, Gross	600.0				600.0				300.0
Effective interest Rate Before Impact of Derivatives	2.96%				2.96%
Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Fixed Interest Rate	0.96%				0.96%
Derivative, Maturity Date					Mar. 31, 2017
First Term Loan Tranche [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative Liability, Notional Amount	300.0				300.0
Derivative, Fixed Interest Rate	1.07%				1.07%
Second Term Loan Tranche [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative Liability, Notional Amount	$ 300.0				$ 300.0
Derivative, Fixed Interest Rate	0.86%				0.86%

[1] Presented net of income tax benefit of $12.2 million and $24.1 million during the three and six months ended June 30, 2013