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

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.

+ References

No definition available.

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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
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- Definition

Aggregate number of common shares reserved for future issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.29)
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- References

No definition available.

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- Definition

Unrecognized cost of unvested share-based compensation awards.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
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- Definition

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.

+ References

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- Definition

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

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
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- Definition

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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- Definition

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).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
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- Definition

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

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
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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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-Publisher FASB
-Name Accounting Standards Codification
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- Definition

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

+ References

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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- Definition

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.

+ References

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- Definition

Number of shares issued in lieu of cash for services contributed to the entity. Number of shares includes, but is not limited to, shares issued for services contributed by vendors and founders.

+ References

No definition available.

+ Details

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Share-Based Compensation (Textual) (Details) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($) shares	Apr. 26, 2017 shares
Share-Based Compensation Plans (Textual) [Abstract]
Share-based compensation expense	$ 17.3	$ 14.7	$ 3.7
Excess tax benefit from share-based compensation	$ 6.1	2.2	0.5
Corporation granted shares of common stock (in shares) \| shares	72,537
Common stock available for future grants under share-based compensation plans (in shares) \| shares	1,681,101			1,750,000
Cash received from option exercises	$ 3.2	$ 2.7	$ 2.3
Shares issued from exercises (in shares) \| shares	621,355	229,055	134,659
Granted after 2012
Share-Based Compensation Plans (Textual) [Abstract]
Stock option vesting period	5 years
Granted prior to 2013
Share-Based Compensation Plans (Textual) [Abstract]
Stock option vesting period	3 years
Stock Options
Share-Based Compensation Plans (Textual) [Abstract]
Stock option expiration period	10 years
Intrinsic value of outstanding in-the-money stock options	$ 26.6	$ 80.4	$ 7.6
Intrinsic value of exercisable in-the-money stock options	$ 21.4
Closing price of common stock (USD per share) \| $ / shares	$ 53.47
Unrecognized compensation expense related to share-based compensation	$ 1.9
Unrecognized compensation expense related to share-based compensation, period for recognition	3 years 6 months
Stock Options \| Non-vested stock options outstanding
Share-Based Compensation Plans (Textual) [Abstract]
Corporation granted options to purchase common stock (in shares) \| shares	132,414	441,167	244,165
Restricted Stock Units
Share-Based Compensation Plans (Textual) [Abstract]
Corporation granted options to purchase restricted stock performance units (in shares) \| shares	169,252
Shares issued from exercises (in shares) \| shares	75,639
Unrecognized compensation expense related to share-based compensation	$ 9.0
Unrecognized compensation expense related to share-based compensation, period for recognition	2 years 8 months
Restricted Stock Units \| Minimum
Share-Based Compensation Plans (Textual) [Abstract]
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) [Abstract]
Restricted stock performance units eligible to vest as a multiple of number of units granted	1.5
Restricted Stock Awards
Share-Based Compensation Plans (Textual) [Abstract]
Unrecognized compensation expense related to share-based compensation	$ 2.2
Unrecognized compensation expense related to share-based compensation, period for recognition	1 year 1 month