Share-Based Compensation - Share-Based Payment Award Activity (Details)	9 Months Ended
Sep. 30, 2019 USD ($) $ / shares shares
Options
Outstanding, beginning of period, in shares \| shares	679,659
Granted, in shares \| shares	121,669
Exercised, in shares \| shares	(104,576)
Forfeited, in shares \| shares	(20,180)
Expired, in shares \| shares	(720)
Outstanding, end of period, in shares \| shares	675,852
Vested and expected to vest, end of period, in shares \| shares	657,968
Exercisable, end of period, in shares \| shares	411,981
Weighted Average Exercise Price
Outstanding, beginning of period, in usd per share \| $ / shares	$ 137.19
Granted, in usd per share \| $ / shares	249.64
Exercised, in usd per share \| $ / shares	85.38
Forfeited, in usd per share \| $ / shares	211.23
Expired, in usd per share \| $ / shares	64.37
Outstanding, end of period, in usd per share \| $ / shares	163.32
Vested and expected to vest, end of period, in usd per share \| $ / shares	161.08
Exercisable, end of period, in usd per share \| $ / shares	$ 120.57
Weighted Average Remaining Contractual Life - in Years
Outstanding, end of period	3 years 8 months 4 days
Vested and expected to vest, end of period	3 years 7 months 13 days
Exercisable, end of period	2 years 5 months 15 days
Aggregate Intrinsic Value of In-The-Money Options
Outstanding, end of period \| $	$ 43,542,167
Vested and expected to vest, end of period \| $	43,364,465
Exercisable, end of period \| $	$ 38,394,292

Share-based Compensation Arrangement by Share-based Payment Award, Options, Aggregate Intrinsic Value [Abstract]

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Share-based Compensation Arrangement by Share-based Payment Award, Options, Weighted Average Exercise Price [Abstract]

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Share-based Compensation Arrangement by Share-based Payment Award, Options, Weighted Average Remaining Contractual Term [Abstract]

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements.

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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Gross number of share options (or share units) granted during the period.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of options outstanding, including both vested and non-vested options.

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-Publisher FASB
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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Amount by which current fair value of underlying stock exceeds exercise price of fully vested and expected to vest options outstanding. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Number of fully vested and expected to vest options outstanding that can be converted into shares under option plan. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted-average exercise price, at which grantee can acquire shares reserved for issuance, for fully vested and expected to vest options outstanding. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options of the plan that expired.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for fully vested and expected to vest options outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Number of share options (or share units) exercised during the current period.

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