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.

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Face (par) amount of debt instrument at time of issuance.

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Contractual interest rate for funds borrowed, under the debt agreement.

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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.

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The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

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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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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.

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Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

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Long-term Debt - Senior Unsecured Credit Facility (Narrative) (Details) - USD ($)	Mar. 31, 2021	Dec. 31, 2020	Aug. 18, 2020	Jun. 25, 2020
Long-term debt
Letters of credit outstanding, amount	$ 400,000
Available borrowing capacity	1,174,600,000
Senior Unsecured Notes 4.00 Percent Due 2031
Long-term debt
Long-term debt, gross	700,000,000	$ 700,000,000
Debt Instrument, Face Amount			$ 200,000,000	$ 500,000,000
$700 million 4.00% senior unsecured notes due January 2030
Long-term debt
Long-term debt, gross	700,000,000	700,000,000
Debt Instrument, Face Amount	$ 700,000,000	$ 700,000,000
Debt instrument, interest rate, stated percentage	4.00%	4.00%	4.00%	4.00%
Senior unsecured credit facility
Long-term debt
Long-term debt, gross	$ 424,000,000.0
Revolving credit facility
Long-term debt
Line of credit facility, maximum borrowing capacity	1,175,000,000	$ 1,175,000,000
Unsecured term loan A-1
Long-term debt
Line of credit facility, maximum borrowing capacity	449,000,000
Outstanding balance on credit facility	224,000,000
Incremental Term Loan A - 2 Facility
Long-term debt
Outstanding balance on credit facility	$ 200,000,000