Earnings Per Share (Details) (USD $) In Thousands, except Share data	3 Months Ended	6 Months Ended
Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Net income	$ 14,701	$ 20,137	$ 29,214	$ 38,279
Denominator for basic earnings per share - weighted-average number of common shares outstanding during the period	60,159,000	62,695,000	60,537,000	63,047,000
Denominator for diluted earnings per share	60,567,000	63,243,000	61,125,000	63,598,000
Basic earnings per share	$ 0.24	$ 0.32	$ 0.48	$ 0.61
Diluted earnings per share	$ 0.24	$ 0.32	$ 0.48	$ 0.60
Options to purchase of common shares	3,700,000	2,400,000	2,900,000	2,400,000
Stock Options [Member]
Incremental common shares attributable to exercise of outstanding dilutive options	313,000	450,000	413,000	457,000
Restricted Shares, Restricted Stock Units And Phantom Stock [Member]
Incremental common shares attributable to outstanding restricted shares, restricted stock units and phantom stock	95,000	98,000	175,000	94,000

Incremental Common Shares Attributable To Outstanding Restricted Shares, Restricted Stock Units And Phantom Stock

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- Definition

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) in the future that were not included in the computation of diluted EPS because to do so would increase EPS amounts or decrease loss per share amounts for the period presented.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 128
-Paragraph 13, 14

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 128
-Paragraph 171

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 128
-Paragraph 40
-Subparagraph c

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- Definition

The amount of net income or loss for the period per each share of common stock outstanding during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 04
-Paragraph 21
-Article 9

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 128
-Paragraph 36, 37, 38

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 20
-Article 5

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 04
-Paragraph 18
-Article 7

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- Definition

The amount of net income or loss for the period per each share of common stock and dilutive common stock equivalents outstanding during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 128
-Paragraph 11, 12, 36

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
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-Publisher SEC
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-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
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- Definition

Aggregate awards of share options and nonvested shares to be issued to an employee under a share-based compensation arrangement are considered options for purposes of computing diluted earnings per share. Such share-based awards shall be considered to be outstanding as of the grant date for purposes of computing diluted earnings per share even though their exercise may be contingent upon vesting. Those share-based awards are included in the diluted Earnings Per Share (EPS) computation even if the employee may not receive (or be able to sell) the stock until some future date. Accordingly, all shares to be issued shall be included in computing diluted EPS if the effect is dilutive. The dilutive effect of share-based compensation arrangements shall be computed using the treasury stock method. If the equity share options or other equity instruments are outstanding for only part of a period, the shares issuable shall be weighted to reflect the portion of the period during which the equity instruments were outstanding.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 128
-Paragraph 20

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- Definition

The portion of consolidated profit or loss for the period, net of income taxes, which is attributable to the parent. If the entity does not present consolidated financial statements, the amount of profit or loss for the period, net of income taxes.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 19
-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Accounting Research Bulletin (ARB)
-Number 51
-Paragraph 38
-Subparagraph d

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-Name Accounting Research Bulletin (ARB)
-Number 51
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-Appendix A

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-Number 51
-Paragraph 38
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Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 04
-Paragraph 20
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Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 130
-Paragraph 10, 15

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Emerging Issues Task Force (EITF)
-Number 87-21

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-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 95
-Paragraph 28, 29, 30

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- Definition

The average number of shares issued and outstanding that are used in calculating diluted EPS, determined based on the timing of issuance of shares in the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 128
-Paragraph 40
-Subparagraph a

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- Definition

Number of [basic] shares, after adjustment for contingently issuable shares and other shares not deemed outstanding, determined by relating the portion of time within a reporting period that common shares have been outstanding to the total time in that period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 128
-Paragraph 171

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