Stock-Based Compensation (Details) (USD $)	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Stock-Based Compensation
Number of stock-based compensation plans	2
Stock Option
Options
Outstanding at the beginning of the period (in shares)	1,432,228
Granted (in shares)	111,147
Exercised (in shares)	(156,665)
Forfeited (in shares)	(2,896)
Outstanding at the end of the period (in shares)	1,383,814
Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 10.34
Granted (in dollars per share)	$ 24.68
Exercised (in dollars per share)	$ 6.13
Forfeited (in dollars per share)	$ 19.36
Outstanding at the end of the period (in dollars per share)	$ 11.95
Assumptions used in determining the fair value of stock options granted for fixed awards with graded vesting schedules
Risk-free interest rate (as a percent)	1.00%
Expected dividend yield (as a percent)	0.00%	0.00%
Weighted average expected volatility (as a percent)	50.00%	50.00%
Expected term	6 years
Weighted average grant-date fair value (in dollars per share)	$ 11.74	$ 8.57
Stock Option \| Minimum
Assumptions used in determining the fair value of stock options granted for fixed awards with graded vesting schedules
Risk-free interest rate (as a percent)		1.20%
Expected term		6 years
Stock Option \| Maximum
Assumptions used in determining the fair value of stock options granted for fixed awards with graded vesting schedules
Risk-free interest rate (as a percent)		1.40%
Expected term		6 years 3 months 18 days
Restricted Stock
Shares
Outstanding at the beginning of the period (in shares)	185,764
Granted (in shares)	69,882
Vested (in shares)	(45,939)
Forfeited (in shares)	(1,562)
Outstanding unvested at the end of the period (in shares)	208,145
Weighted-Average Grant Date Fair Value
Outstanding at the beginning of the period (in dollars per share)	$ 19.54
Granted (in dollars per share)	$ 24.68
Vested (in dollars per share)	$ 19.50
Forfeited (in dollars per share)	$ 19.16
Outstanding unvested at the end of the period (in dollars per share)	$ 21.27
Shares received as payment for withholding taxes due by holders of awards	11,449
Performance Awards
Shares
Outstanding at the beginning of the period (in shares)	74,923
Granted (in shares)	46,106
Outstanding unvested at the end of the period (in shares)	121,029
Weighted-Average Grant Date Fair Value
Outstanding at the beginning of the period (in dollars per share)	$ 20.51
Granted (in dollars per share)	$ 24.68
Outstanding unvested at the end of the period (in dollars per share)	$ 22.10

Represents the number of share-based compensation plans approved by the entity's shareholders.

No definition available.

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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).

+ References

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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.

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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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-Publisher FASB

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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

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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- Definition

Expected term of share-based compensation awards, 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

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-Name Accounting Standards Codification

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-SubTopic 10

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-Name Staff Accounting Bulletin (SAB)

-Number Topic 14

-Section D

-Subsection 2

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The risk-free interest rate assumption that is used in valuing an option on its own shares.

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- Definition

The range of expected volatilities used and the weighted-average expected volatility for an entity using a valuation technique with different volatilities during the contractual term.

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- Definition

The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

+ References

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- Definition

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

+ References

No definition available.

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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- Definition

The number of shares reserved for issuance under stock option agreements awarded under the plan that validly exist and are outstanding as of the balance sheet date, including vested options.

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-Publisher FASB

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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- Definition

Weighted average price at which option holders acquired shares when converting their stock options into shares.

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No definition available.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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No definition available.

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Weighted average price at which grantees can acquire the shares reserved for issuance on stock options awarded.

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No definition available.

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For net-share settlement of share-based awards when the employer settles employees' income tax withholding obligations, this element represents the number of shares the employees use to repay the employer.

+ References

No definition available.

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Number of share options (or share units) exercised during the current period.

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