Fair Value of Financial Instruments - Senior Notes - Narrative (Details) - 4.50% Senior Notes - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Fair Value Disclosure of Liabilities Not Measured at Fair Value [Line Items]
Senior notes, gross carrying amount	$ 600.0	$ 600.0
Senior Notes
Fair Value Disclosure of Liabilities Not Measured at Fair Value [Line Items]
Debt instrument, interest rate (percentage)	4.50%	4.50%
Senior notes, estimated fair value	$ 624.0	$ 625.5

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

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-Publisher FASB
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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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Fair value portion of notes payable.

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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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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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