Debt (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Notes Payable to Bank, Noncurrent	$ 355,000us-gaap_NotesPayableToBankNoncurrent	$ 370,000us-gaap_NotesPayableToBankNoncurrent
Bank credit facility due March 2016	250,000us-gaap_LineOfCredit	235,000us-gaap_LineOfCredit
Total debt	3,053,636us-gaap_LongTermDebt	3,054,725us-gaap_LongTermDebt
Less current maturities	(90,960)us-gaap_LongTermDebtCurrent	(90,931)us-gaap_LongTermDebtCurrent
Long-term Debt and Capital Lease Obligations, Current	(90,960)	(90,931)
Total long-term debt	2,962,676us-gaap_LongTermDebtNoncurrent	2,963,794us-gaap_LongTermDebtNoncurrent
Unsecured Debt
Debt Instrument [Line Items]
Unamortized pricing discounts and other	(2,752)	(2,905)
Unsecured Debt \| April 2016
Debt Instrument [Line Items]
Senior Notes	197,377	197,377
Unsecured Debt \| June 2017
Debt Instrument [Line Items]
Senior Notes	295,000	295,000
Unsecured Debt \| October 2018
Debt Instrument [Line Items]
Senior Notes	250,000	250,000
Unsecured Debt \| November 2020
Debt Instrument [Line Items]
Senior Notes	200,000	200,000
Unsecured Debt \| November 2021
Debt Instrument [Line Items]
Senior Notes	150,000	150,000
Unsecured Debt \| January 2022
Debt Instrument [Line Items]
Senior Notes	425,000	425,000
Unsecured Debt \| May 2024
Debt Instrument [Line Items]
Senior Notes	550,000	550,000
Unsecured Debt \| April 2027
Debt Instrument [Line Items]
Senior Notes	200,000	200,000
Revolving Credit Facility
Debt Instrument [Line Items]
Bank credit facility due March 2016	250,000	235,000
Capital Lease Obligations
Debt Instrument [Line Items]
Obligations under capital leases	179,824	181,002
Mortgages
Debt Instrument [Line Items]
Mortgage notes and other debt, maturities through 2047	$ 4,187	$ 4,251

Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal through the balance sheet date.

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The amount of debt discount (net of debt premium) that was originally recognized at the issuance of the instrument that has yet to be amortized.

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount of long-term debt and capital leases due within one year or the normal operating cycle, if longer.

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Amount of long-term debt, after unamortized discount or premium, scheduled to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Carrying amount of long-term debt, net of unamortized discount or premium, excluding amounts to be repaid within one year or the normal operating cycle, if longer (current maturities). Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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The total amount due within more than 12 month, or the operating cycle if longer, on all notes payable to banks paid on an installment. This can include the amount of any loans from the applicant firm. This does not, however, include any mortgage balances.

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Including the current and noncurrent portions, the carrying value of notes payable which were initially due after one year or beyond the normal operating cycle, if longer, and which are not otherwise defined in the taxonomy.

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Including the current and noncurrent portions, carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer). Senior note holders are paid off in full before any payments are made to junior note holders.

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