Shareholders' Equity (Details) (USD $)	1 Months Ended	9 Months Ended	3 Months Ended
Jun. 30, 2011	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011 Common Stock
Stockholders' Equity
Amount of common stock authorized to repurchase	$ 300,000,000
Number of shares of common stock repurchased (in shares)				755,517
Amount for which shares of stock are repurchased		$ 27,036,000	$ 35,858,000	$ 27,100,000
Average price paid per share of common stock repurchased (in dollars per share)				$ 35.78

Represents the average price paid for each share purchased during the period under stock repurchase plan.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

Number of shares that have been repurchased and retired during the period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644

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

-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 12

-Paragraph 10

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 29, 30

-Article 5

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- Definition

Equity impact of the value of stock that has been repurchased and retired during the period. The excess of the purchase price over par value can be charged against retained earnings (once the excess is fully allocated to additional paid in capital).

+ References

+ Details

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- Definition

The amount authorized by an entity's Board of Directors under a stock repurchase plan.

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