Long-Term Debt, Finance Lease and Deferred Financing Obligations - Senior Notes (Details) - Senior Notes - 4.400% Senior Notes due 2024 - USD ($) $ in Millions		12 Months Ended
Sep. 22, 2017	Dec. 31, 2020	Dec. 31, 2019
Debt
Debt instrument, face amount	$ 400.0
Stated interest rate (as a percent)	4.40%
Debt instrument, repurchased face amount		$ 28.9	$ 11.1
Gain (loss) on repurchase of debt instrument		(0.7)	(0.3)
Long-term debt		$ 359.6	$ 388.4
Debt instrument, maturity date		Sep. 22, 2024
Redemption price of the principal amount redeemed (as a percent)	100.00%

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

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- Definition

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

+ References

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Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

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Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

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Face (par) amount of the original debt instrument that was repurchased.

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Amount of gain (loss) from the difference between the repurchase price of a debt instrument initially issued by the entity and the net carrying amount of the debt at the time of its repurchase.

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No definition available.

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- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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