Debt (Narrative) (Details) - USD ($)	Jun. 30, 2018	Dec. 31, 2017
Letter of Credit [Member]
Debt Instrument [Line Items]
Credit facility amount	$ 49,600,000
Line of credit availability	215,000,000
Term Loan A [Member]
Debt Instrument [Line Items]
Line of credit availability	600,000,000	$ 600,000,000
Term Loan B [Member]
Debt Instrument [Line Items]
Line of credit availability	250,000,000	250,000,000
Bi-lateral Facility [Member] \| Letter of Credit [Member]
Debt Instrument [Line Items]
Credit facility amount	13,400,000
Line of credit availability	25,000,000	25,000,000
Tax-Exempt Industrial Development Bond [Member]
Debt Instrument [Line Items]
Long-term debt outstanding	35,000,000	35,000,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit availability	200,000,000	200,000,000
Letter of credit maximum sublimit	150,000,000	150,000,000
Amount outstanding	0	0
Securitization Facility [Member] \| Letter of Credit [Member]
Debt Instrument [Line Items]
Credit facility amount	36,200,000
Line of credit availability	40,000,000
Letters of credit issued classified as restricted cash		6,600,000
Senior Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility amount	$ 1,050,000,000	$ 1,050,000,000

Letter of credit maximum sublimit amount.

No definition available.

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- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

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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Period Type:	instant

- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

+ References

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

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- Definition

Amount of cash and cash equivalents restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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