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Share based compensation arrangement by share based payment award options grants in period aggregate grant date fair value.

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Share based compensation arrangement by share based payment award number of in-the-money options outstanding and exercisable.

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

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Amount of cost to be recognized for option under share-based payment arrangement.

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

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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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Discount rate from fair value on purchase date that participants pay for shares.

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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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Number of shares authorized for issuance under share-based payment arrangement.

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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

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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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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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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Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

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Number of shares issued during the period as a result of an employee stock purchase plan.

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Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
	May 25, 2017	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized				18,650,000
Number of shares, outstanding		3,785,941	5,318,759	6,839,417	6,342,526
Number of shares available for grant		1,000,000	2,300,000
Options, aggregate intrinsic value		$ 146.3
Options, exercisable, intrinsic value		$ 71.9
Common stock closing price (in dollars per share)		$ 53.84
Options outstanding and exercisable (in shares)		1,600,000
Options exercised during period, intrinsic value		$ 68.6	$ 35.3	$ 29.3
Proceeds from stock options exercised		18.4	12.4	8.6
Fair value of options granted		7.5	5.6	6.9
Fair value of options vested		$ 5.2	$ 5.5	$ 5.5
Common stock issuance ESPP plan (in shares)		138,309	141,908	113,503
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation expense		$ 6.0	$ 6.8	$ 5.4
Unrecognized stock based compensation		$ 5.7
Unrecognized stock based compensation, weighted average period		1 year 10 months 24 days
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation expense		$ 0.9	0.6	0.2
Discount from market price (as a percent)	15.00%
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation expense		3.4	$ 2.6	$ 1.3
Unrecognized stock based compensation		$ 3.3
Unrecognized stock based compensation, weighted average period		1 year 9 months 18 days
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period		3 years
Minimum \| Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period		5 years
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period		4 years
Maximum \| Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period		7 years