Debt and Lease Obligations (Senior Credit Facility) (Details) (USD $)	12 Months Ended					12 Months Ended		9 Months Ended	12 Months Ended						12 Months Ended		12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Interest Rate Swap [Member] Designated as Hedging Instrument [Member]	Dec. 31, 2012 Interest Rate Swap [Member] Designated as Hedging Instrument [Member]	Dec. 31, 2013 Term Loan Facility [Member]	Dec. 31, 2012 Term Loan Facility [Member]	Sep. 30, 2013 Senior Credit Facility [Member]	Dec. 31, 2013 Senior Credit Facility [Member]	Dec. 31, 2012 Senior Credit Facility [Member]	Dec. 31, 2013 Revolving Credit Facility [Member]	Oct. 04, 2013 Revolving Credit Facility [Member]	Oct. 03, 2013 Revolving Credit Facility [Member]	Dec. 31, 2012 Revolving Credit Facility [Member]	Dec. 31, 2013 Term Loan Or Revolving Credit Facility [Member]	Dec. 31, 2013 Swingline loan [Member]	Dec. 31, 2012 Prior Credit Agreement [Member]	Dec. 31, 2011 Prior Credit Agreement [Member]	Jun. 15, 2012 Bridge Loan [Member]	Dec. 31, 2013 Letter of Credit [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Face Amount						$ 400,000,000
Debt Instrument, Maturity Date								Oct. 04, 2018
Line of Credit Facility, Maximum Borrowing Capacity												1,000,000,000	850,000,000			30,000,000				300,000,000
Letters of Credit Outstanding, Amount									106,100,000	152,200,000
Credit agreement maximum borrowing capacity increase in additional borrowings															400,000,000
Line of Credit Facility, Amount Outstanding											0
Line of Credit Facility, Current Borrowing Capacity											893,900,000			697,800,000
Maximum permitted leverage ratio, Debt to Total Consolidated EBITDA									3.25
Minimum interest coverage, consolidated EBITDA to Total Interest Expense									3.25
Line of Credit Facility, Commitment Fee Percentage									0.175%
Repayments of Long-term Debt	25,000,000	480,000,000	25,000,000			25,000,000	5,000,000										12,500,000	25,000,000
Credit Facilities Scheduled Repayments Due in Next Four Quarters						10,000,000
Derivative, notional amount				140,000,000	275,000,000
Bridge Loan																			$ 250,000,000
Maturity Period of Bridge Loan																			364 days