Share-Based Compensation Restricted stock units (Details) (USD $)	9 Months Ended
Sep. 30, 2014
Restricted Stock Units (RSUs) [Member]
Transactions under the terms of the LTSIP - shares [Roll Forward]
Balance at December 31, 2013	316,268
Granted	353,540
Vested	(131,007)
Forfeited	(10,225)
Balance at September 30, 2014	528,576
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]
Balance at December 31, 2013	$ 23.62
Granted	$ 23.60
Vested	$ 23.64
Forfeited	$ 23.60
Balance at September 30, 2014	$ 23.60
Share-based awards other than options, additional disclosures [Abstract]
Number of shares of common stock to be issued for each vested restricted stock unit (RSU)	1
Vesting period for share-based award (in years)	3 years
Weighted-average remaining vesting period of share-based awards (in months)	15 months
Weighted-average price of deferred restricted stock units outstanding	$ 23.60
Restricted Stock Units (RSUs) [Member] \| Minimum [Member]
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]
Balance at December 31, 2013	$ 22.17
Granted	$ 22.81
Vested	$ 22.17
Forfeited	$ 23.60
Balance at September 30, 2014	$ 22.17
Share-based awards other than options, additional disclosures [Abstract]
Weighted-average price of deferred restricted stock units outstanding	$ 22.17
Restricted Stock Units (RSUs) [Member] \| Maximum [Member]
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]
Balance at December 31, 2013	$ 25.44
Granted	$ 24.70
Vested	$ 25.44
Forfeited	$ 23.62
Balance at September 30, 2014	$ 24.70
Share-based awards other than options, additional disclosures [Abstract]
Weighted-average price of deferred restricted stock units outstanding	$ 24.70
Deferred Restricted Stock Units (RSUs) [Member]
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]
Balance at September 30, 2014	$ 23.60
Share-based awards other than options, additional disclosures [Abstract]
Number of shares of common stock to be issued for each vested restricted stock unit (RSU)	1
Vesting period for share-based award (in years)	1 year
Weighted-average remaining vesting period of share-based awards (in months)	5 months
Number of deferred restricted stock units outstanding (in shares)	17,355
Weighted-average price of deferred restricted stock units outstanding	$ 23.60

Number of shares of common stock to be issued for each vested restricted stock unit (RSU)

No definition available.

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

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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.

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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).

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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).

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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.

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- Definition

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.

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- Definition

Weighted average remaining contractual term for equity-based awards excluding options, 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 equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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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.

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- Definition

Number of equity instruments other than options outstanding, including both vested and non-vested instruments.

+ 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)(1)(i)

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

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)(ii)

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

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