Commitments and Contingencies (Details) (USD $)	1 Months Ended	3 Months Ended	12 Months Ended
	Jan. 31, 2013	Mar. 31, 2013	Dec. 31, 2012 Years	Dec. 31, 2011	Dec. 31, 2010
Commitments and Contingencies [Abstract]
Operating lease expense			$ 19,300,000	$ 20,400,000	$ 16,200,000
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2012			16,200,000
2013			12,500,000
2014			9,000,000
2015			4,100,000
2016			1,600,000
Thereafter			1,500,000
Total			44,900,000
Operating Leases, Future Minimum Payments Receivable [Abstract]
Contractual minimum revenue, Current			135,200,000
Contractual minimum revenue, in Two Years			106,500,000
Contractual minimum revenue, in Three Years			70,700,000
Contractual minimum revenue, in Four Years			49,600,000
Contractual minimum revenue, in Five Years			34,100,000
Asset Retirement Obligation [Abstract]
Balance, Beginning of Period	7,100,000	7,100,000	5,400,000	5,100,000
Liabilities Incurred			200,000	200,000
Revision to cashflow estimate			1,100,000	(200,000)
Accretion Expense			400,000	300,000
Balance, End of Period			7,100,000	5,400,000	5,100,000
Letters of Credit Outstanding, Amount			6,300,000
Long-term Purchase Commitments, Range of Years, Minimum			1
Long-Term Purchase Commitments, Range of Years, Maximum			3
Long-term Purchase Commitment, Amount			120,000,000	66,000,000
Maximum payout of contingent compensation plan			100,000,000
Payoutofcontingentcompensationplanthresholdvalue			1,000,000,000
Common Stock, Shares, Issued	18,975,000
Expected future payments under contingent compensation plan, lower range		40,000,000
Expected future payments under contingent compensation plan, upper range		$ 50,000,000