Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Unrecognized cost of unvested share-based compensation awards.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

Amount of cash inflow from exercise of stock options granted under share-based compensation arrangement.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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

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Total number of shares issued during the period, including shares forfeited, as a result of Restricted Stock Awards.

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Gross number of shares (or other type of equity) issued during the period as a result of any equity-based compensation plan other than an employee stock ownership plan (ESOP). Shares issued could result from the issuance of restricted stock, the exercise of stock options, stock issued under employee stock purchase plans, and/or other employee benefit plans.

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

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Share-Based Compensation - Additional Information (Detail) - USD ($) shares in Millions, $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option exercised				1.0	0.3
Cash received from stock option exercises				$ 8.3	$ 2.3
Common stock issued pursuant to the vesting of restricted stock units (RSUs)				0.3	0.3
Common stock issued pursuant to the vesting of performance-based restricted stock units (PRSUs)		0.2
Stock options granted				1.6	1.0
Share-based compensation expense	$ 10.2		$ 6.3	$ 29.1	$ 20.5
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost	50.9			$ 50.9
Stock vesting period				2 years 9 months 19 days
Stock vesting period				4 years	4 years
Share-based compensation expense				$ 18.7	$ 13.1
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost	32.7			$ 32.7
Stock vesting period				2 years 10 months 24 days
Stock vesting period				4 years	4 years
Share-based compensation expense				$ 10.4
Restricted stock units granted				0.6	0.3
Performance-based RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost	$ 7.5			$ 7.5
RSU with performance-based vesting requirements outstanding	0.2			0.2
Stock vesting period					4 years
Share-based compensation expense					$ 7.4
Restricted stock units granted					0.2