Fair Value of Financial Instruments (Senior Notes) (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
4.50% Senior Notes [Member]
Fair Value Disclosure of Liabilities Not Measured at Fair Value [Line Items]
Senior Notes, gross carrying amount	$ 600.0
4.50% Senior Notes [Member] \| Senior Notes [Member]
Fair Value Disclosure of Liabilities Not Measured at Fair Value [Line Items]
Debt instrument, interest rate (percentage)	4.50%
Debt instrument, maturity date	Aug. 15, 2028
Senior Notes, estimated fair value	$ 625.5
4.875% Senior Notes [Member]
Fair Value Disclosure of Liabilities Not Measured at Fair Value [Line Items]
Senior Notes, gross carrying amount		$ 400.0
4.875% Senior Notes [Member] \| Senior Notes [Member]
Fair Value Disclosure of Liabilities Not Measured at Fair Value [Line Items]
Debt instrument, interest rate (percentage)	4.875%
Debt instrument, maturity date	Mar. 15, 2023
Senior Notes, estimated fair value		$ 404.5

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(2))
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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

Fair value portion of notes payable.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
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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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
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