Share-Based Compensation - Restricted Stock Awards and Performance Share Awards Activity (Details) - $ / shares	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Restricted Stock Awards and Performance Share Awards
Outstanding at beginning of year (in shares)	434,641	657,724	628,642
Granted (in shares)	178,150	170,502	206,922
Released (in shares)	(275,318)	(372,075)	(154,878)
Forfeited (in shares)	(18,908)	(21,510)	(22,962)
Outstanding at end of year (in shares)	318,565	434,641	657,724
Weighted-Average Grant Date Fair Value
Outstanding at beginning of year (in USD per share)	$ 151.52	$ 93.45	$ 77.70
Granted (in USD per share)	265.06	204.26	150.60
Released (in USD per share	133.43	73.71	107.22
Forfeited (in USD per share)	199.04	141.29	88.77
Outstanding at end of year (in USD per share)	$ 228.08	$ 151.52	$ 93.45
Restricted Stock \| Nonemployee
Restricted Stock Awards and Performance Share Awards
Granted (in shares)	6,314	7,371	7,980
Performance Share Awards
Restricted Stock Awards and Performance Share Awards
Outstanding at beginning of year (in shares)	170,749	259,727	265,747
Granted (in shares)	98,820	150,224	59,849
Released (in shares)	(131,943)	(231,513)	(57,074)
Forfeited (in shares)	(11,604)	(7,689)	(8,795)
Outstanding at end of year (in shares)	126,022	170,749	259,727
Weighted-Average Grant Date Fair Value
Outstanding at beginning of year (in USD per share)	$ 144.47	$ 86.41	$ 77.04
Granted (in USD per share)	239.79	206.04	146.83
Released (in USD per share	160.18	120.86	107.31
Forfeited (in USD per share)	194.23	102.42	81.07
Outstanding at end of year (in USD per share)	$ 199.77	$ 144.47	$ 86.41

Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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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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