Stock-Based Compensation - Stock-Based Compensation Information (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Per share intrinsic value of non-vested stock granted (in dollars per share)	$ 130.89	$ 75.73	$ 86.84
Weighted average per share discount from market value for shares purchased (in dollars per share)	$ 22.97	$ 17.83	$ 13.10
Fair value of non-vested stock that vested during the period (in millions)	$ 108.5	$ 92.0	$ 92.0
Tax benefit recognized in Consolidated Statements of Operations (in millions)	3.7	2.7	3.5
Cash received from options exercised and shares purchased under all share-based arrangements (in millions)	14.8	11.3	10.6
Tax deduction realized related to stock options exercised (in millions)	13.6	9.8	9.0
Selling, General and Administrative Expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation recognized in Consolidated Statements of Operations, as a component of selling, general and administrative expense (in millions)	$ 23.2	$ 16.2	$ 13.4

The weighted average discount per share for compensation expense recognized under the 2009 ESPP.

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Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Amount of tax benefit for recognition of expense of award under share-based payment arrangement.

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Amount of tax benefit from exercise of option under share-based payment arrangement.

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Amount of cash inflow from issuance of shares under share-based payment arrangement. Includes, but is not limited to, option exercised.

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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The grant-date intrinsic value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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