Stockholders' Equity 1 (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended	12 Months Ended
Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2009	Sep. 30, 2009	Jun. 30, 2009	Mar. 31, 2009	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Dividends Declared [Abstract]
Shareholder Record Date	Dec. 30, 2011	Sep. 30, 2011	Jun. 24, 2011	Mar. 25, 2011	Dec. 31, 2010	Sep. 24, 2010	Jun. 25, 2010	Mar. 26, 2010	Dec. 25, 2009	Sep. 25, 2009	Jun. 26, 2009	Mar. 27, 2009
Date Paid	Jan. 13, 2012	Oct. 14, 2011	Jul. 08, 2011	Apr. 08, 2011	Jan. 14, 2011	Oct. 08, 2010	Jul. 09, 2010	Apr. 09, 2010	Jan. 08, 2010	Oct. 09, 2009	Jul. 10, 2009	Apr. 10, 2009
Amount Per Share	$ 0.15	$ 0.15	$ 0.15	$ 0.15	$ 0.15	$ 0.15	$ 0.15	$ 0.15	$ 0.15	$ 0.15	$ 0.15	$ 0.15	$ 0.60	$ 0.60	$ 0.60
Amount Paid	$ 18,726	$ 18,712	$ 18,709	$ 18,700	$ 18,690	$ 18,674	$ 18,672	$ 18,665	$ 18,657	$ 18,610	$ 18,607	$ 18,607	$ 74,811	$ 74,668	$ 74,424

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Aggregate dividends paid during the period for each share of common stock outstanding.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.3-04)

-URI http://asc.fasb.org/extlink&oid=6959260&loc=d3e187085-122770

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- Definition

The day, month, and year (YYYY-MM-DD) that the dividend declared as of or prior to the financial reporting date will be paid in the subsequent period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 50

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4304-108586

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- Definition

The date as of when a holder must own the stock to be entitled to the dividend. The ex-dividend date is generally 3 days before the record date.

+ References

No definition available.

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- Definition

The cash outflow from the distribution of an entity's earnings in the form of dividends to common shareholders.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 15

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3291-108585

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 18

-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 Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 20

-Subparagraph 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 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Financing Activities

-URI http://asc.fasb.org/extlink&oid=6513228

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