Price at closing of a single share of a number of saleable stocks of a company.

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- Definition

Unrecognized cost of unvested options awarded to employees as compensation.

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Weighted average period over which unrecognized compensation related to stock options 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

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

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No definition available.

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- Definition

Share based compensation arrangement by share based payment awards number of units eligible to vest as a multiple of number of units granted.

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- Definition

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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- Definition

Aggregate number of common shares reserved for future issuance.

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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

Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

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- Definition

Amount of tax benefit from exercise of stock options granted under share-based compensation arrangement.

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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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- Definition

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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No definition available.

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The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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- Definition

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

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- Definition

Number of share instruments newly issued under a share-based compensation plan.

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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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- Definition

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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Share-Based Compensation - Textual (Details) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($) $ / shares shares	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) $ / shares shares	Jun. 30, 2017 USD ($) shares	Apr. 26, 2017 shares
Share-based Compensation Plans (Textual)
Share-based compensation expense	$ 2.4	$ 3.2	$ 4.1	$ 7.0
Excess tax benefit from share-based compensation transactions	$ 0.4	0.2	1.8	6.4
Cash received from option exercises			$ 2.2	1.0
Stock Incentive Plan of 2015
Share-based Compensation Plans (Textual)
Common stock available for future grants under share-based compensation plans (in shares) \| shares	1,326,333		1,326,333
Stock Incentive Plan of 2017
Share-based Compensation Plans (Textual)
Number of shares authorized under stock incentive plan (in shares) \| shares					1,750,000
Stock Incentive Plans After 2012
Share-based Compensation Plans (Textual)
Vesting period			5 years
Stock Incentive Plans Prior To 2013
Share-based Compensation Plans (Textual)
Vesting period			3 years
Stock options
Share-based Compensation Plans (Textual)
Stock option award vesting period			10 years
Outstanding in-the-money stock options, intrinsic value		$ 24.6		$ 24.6
Stock issued from exercises (in shares) \| shares			162,065	511,144
Restricted stock units
Share-based Compensation Plans (Textual)
Corporation granted options to purchase restricted stock performance units (in shares) \| shares			295,995
Stock issued from exercises (in shares) \| shares			63,154
Unrecognized compensation expense	$ 20.3		$ 20.3
Unrecognized compensation expense, period for recognition			3 years 5 months
Restricted stock units \| Minimum
Share-based Compensation Plans (Textual)
Restricted stock performance units eligible to vest as a multiple of number of units granted			0.5
Restricted stock units \| Maximum
Share-based Compensation Plans (Textual)
Restricted stock performance units eligible to vest as a multiple of number of units granted			1.5
Equity Option
Share-based Compensation Plans (Textual)
Weighted-average remaining contractual terms for outstanding stock options			6 years 4 months
Weighted-average remaining contractual terms for exercisable stock options			5 years 7 months
Outstanding in-the-money stock options, intrinsic value	19.8		$ 19.8
Exercisable in-the-money stock options, intrinsic value	$ 15.6		$ 15.6
Closing price of common stock (dollars per share) \| $ / shares	$ 55.67		$ 55.67
Unrecognized compensation expense	$ 1.6		$ 1.6
Unrecognized compensation expense, period for recognition			3 years 10 days
Restricted stock awards
Share-based Compensation Plans (Textual)
Unrecognized compensation expense	$ 1.3		$ 1.3
Unrecognized compensation expense, period for recognition			7 months 15 days