Share-Based Compensation Summary of the Corporation's Restricted Stock Unit Activity and Related Information (Details) (Restricted Stock Units (RSUs), USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014
Service-Based Units
Non-vested balance at January 1, 2014	331
Granted (Shares)	15
Converted (Shares)	(41)
Vested (Shares)	0
Non-vested balance at December 31, 2014	387
Non-vested balance at January 1, 2014 (Weighted Average Grant-Date Fair Value)	$ 34.01
Granted (Weighted Average Grant-Date Fair Value)	$ 49.30
Converted (Weighted Average Grant-Date Fair Value)	$ 33.79
Vested (Weighted Average Grant-Date Fair Value)	$ 0
Non-vested balance at December 31, 2014 (Weighted Average Grant-Date Fair Value)	$ 34.58
Performance-Based Units
Non-vested balance at January 1, 2014	124
Granted (Shares)	240
Converted (Shares)	(41)
Vested (Shares)	(4)
Non-vested balance at December 31, 2014	319
Non-vested balance at January 1, 2014 (Weighted Average Grant-Date Fair Value)	$ 33.79
Granted (Weighted Average Grant-Date Fair Value)	$ 49.51
Converted (Weighted Average Grant-Date Fair Value)	$ 33.79
Vested (Weighted Average Grant-Date Fair Value)	$ 49.51
Non-vested balance at December 31, 2014 (Weighted Average Grant-Date Fair Value)	$ 45.44

Share-Based Compensation Summary of the Corporation's Restricted Stock Unit Activity and Related Information (Details) (Restricted Stock Units (RSUs), USD $)
In Thousands, except Per Share data, unless otherwise specified

12 Months Ended

Dec. 31, 2014

Non-vested balance at January 1, 2014

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Granted (Shares)

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Converted (Shares)

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Non-vested balance at December 31, 2014

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Non-vested balance at January 1, 2014 (Weighted Average Grant-Date Fair Value)

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Granted (Weighted Average Grant-Date Fair Value)

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Converted (Weighted Average Grant-Date Fair Value)

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Vested (Weighted Average Grant-Date Fair Value)

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Non-vested balance at December 31, 2014 (Weighted Average Grant-Date Fair Value)

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Performance-Based Units

Non-vested balance at January 1, 2014

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Granted (Shares)

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Converted (Shares)

Vested (Shares)

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Non-vested balance at December 31, 2014

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Non-vested balance at January 1, 2014 (Weighted Average Grant-Date Fair Value)

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Granted (Weighted Average Grant-Date Fair Value)

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Converted (Weighted Average Grant-Date Fair Value)

Vested (Weighted Average Grant-Date Fair Value)

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Non-vested balance at December 31, 2014 (Weighted Average Grant-Date Fair Value)

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- Definition

share-based compensation arrangement by share-based payment awards, equity instrument other than options, converted in period, weighted average grant date fair value

+ References

No definition available.

+ Details

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- Definition

Share-Based compensation Arrangements by share-Based Payment award, Equity Instrument Other than Options, Converted from performance based unit to service-based unit In Period

+ References

No definition available.

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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)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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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

+ Details

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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

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)(i)-(ii)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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- Definition

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+ 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)(i)-(ii)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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- Definition

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

+ 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)(2)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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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

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)(2)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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