Stock Option Plan (Details Textual) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010 Y	Dec. 31, 2009
Stock Option Plan (Textual) [Abstract]
Maximum term of stock options	10 years
Weighted average fair value per share of options granted	$ 22.55	$ 16.13	$ 13.80
Total fair value of options vested	$ 4,981	$ 7,674	$ 8,148
Total intrinsic value of options exercised	57,304	16,817	5,036
Total unrecognized compensation cost related to non-vested share-based compensation arrangements		$ 46,713
Expected weighted average number of years over which unrecognized compensation cost related to non-vested share-based compensation arrangements will be recognized		1.36
Equity Incentive Plan 2009 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Adoption date of 2009 Equity Incentive Plan	May 2009
Number of shares of common stock reserved for issuance	3,635,000
Remaining number of shares of common stock available for issuance	2,218,021
Performance Based Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Service-based awards vesting period	The total number of shares that may vest is determined upon the earnings per share for the grant year with the determined number of shares then vesting annually over the following three and a third years.
Vesting period of performance-based awards	3 years 4 months
Total number of non-vested performance based restricted stock awards outstanding	41,774
Service Based Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Service-based awards vesting period	four years contingent only on the employees' continued employment

The date of adoption of an equity incentive plan based on approval by a company's shareholders.

No definition available.

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- Definition

The maximum term for stock options under an approved equity incentive plan.

+ References

No definition available.

+ Details

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- Definition

The total fair value of stock options that vested during the period.

+ References

No definition available.

+ Details

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- Details

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- Definition

As of the balance sheet date, the aggregate unrecognized cost of equity-based awards made to employees under equity-based compensation awards that have yet to vest.

+ References

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- Definition

The weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, using a decimal to express in number of years.

+ References

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- Definition

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).

+ References

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- Definition

Description of award terms as to how many shares or portion of an award are no longer contingent on satisfaction of either a service condition, market condition or a performance condition, thereby giving the employee the legal right to convert the award to shares, to sell the shares, and be entitled to the cash proceeds of such sale. For example, vesting may be expressed as being 25 percent of the shares under option on each anniversary of the grant date.

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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 Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph b(2)(a)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph b(2)(b)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: 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 maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

+ References

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- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

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

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- Definition

The total accumulated difference between fair values of underlying shares on dates of exercise and exercise price on options which were exercised (or share units converted) into shares during the reporting period under the plan.

+ References

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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.

+ References

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