Employee Stock Plans - Stock Option Activity Table (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Payment Arrangement [Abstract]
Shares outstanding	1,520,917	1,631,017
Shares outstanding, weighted-average exercise price	$ 73.68	$ 69.83
Shares granted	319,438
Shares granted, weighted-average exercise price	$ 79.22
Shares exercised	(353,206)
Shares exercised, weighted-average exercise price	$ 59.56
Shares forfeited	(76,332)
Shares forfeited, weighted-average exercise price	$ 79.87
Shares exercisable	768,112
Shares exercisable, weighted-average exercise price	$ 67.72
Shares outstanding, weighted-average remaining contractual life	81 months
Shares exercisable, weighted-average remaining contractual life	65 months
Shares outstanding, aggregate intrinsic value	$ 35,917
Shares exercisable, aggregate intrinsic value	22,724
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Total Intrinsic Value	8,211	$ 9,346	$ 5,368
Proceeds from exercise of stock options	$ 21,037	$ 16,911	$ 8,819

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Amount of cash inflow from exercise of option under share-based payment arrangement.

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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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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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

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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 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 exercisable or convertible options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the 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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