Stock Compensation Plans (Summary of Activity for Time-Based and Performance-Based RSUs) (Details)	9 Months Ended
Sep. 30, 2018 $ / shares shares
Time-Based RSUs
Shares
Outstanding, beginning of period (in shares) \| shares	1,166,580
Granted (in shares) \| shares	418,940
Vested (in shares) \| shares	(343,506)
Forfeited (in shares) \| shares	(105,174)
Outstanding, end of period (in shares) \| shares	1,136,840
Weighted-Average Grant Date Fair Value
Outstanding, beginning of period (in dollars per share) \| $ / shares	$ 42.00
Granted (in dollars per share) \| $ / shares	67.15
Vested (in dollars per share) \| $ / shares	39.81
Forfeited (in dollars per share) \| $ / shares	50.17
Outstanding, end of period (in dollars per share) \| $ / shares	$ 51.17
Performance-Based RSUs
Shares
Outstanding, beginning of period (in shares) \| shares	424,299
Granted (in shares) \| shares	120,286
Vested (in shares) \| shares	(133,295)
Forfeited (in shares) \| shares	0
Outstanding, end of period (in shares) \| shares	411,290
Weighted-Average Grant Date Fair Value
Outstanding, beginning of period (in dollars per share) \| $ / shares	$ 41.44
Granted (in dollars per share) \| $ / shares	70.13
Vested (in dollars per share) \| $ / shares	41.15
Forfeited (in dollars per share) \| $ / shares	0.00
Outstanding, end of period (in dollars per share) \| $ / shares	$ 49.93

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(3)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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- Definition

Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

+ References

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-Publisher FASB
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-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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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

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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-Paragraph 2
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- Definition

The weighted average fair value at grant date for nonvested equity-based awards issued 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

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- Definition

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.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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-Paragraph 2
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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

+ References

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-Publisher FASB
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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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-Publisher FASB
-Name Accounting Standards Codification
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- Definition

The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

+ References

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