Stock-Based Compensation (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended	6 Months Ended
Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Stock-Based Compensation [Abstract]
Stock-based compensation expense	$ 2,218	$ 1,191	$ 3,911	$ 2,490
Total income tax benefit recognized			1,076	739
Restricted shares granted			33,147
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of new awards granted (in years)			3
Weighted-average grant date fair value (in dollars per share)			$ 43.15
Fair value of shares vested			$ 301	$ 623

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.

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The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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Description of the period of time over 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, which may be expressed in a variety of ways (for example, in years, month and year).

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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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The total fair value of equity-based awards 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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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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