Dividends (Dividends Paid) (Details) (USD $)	3 Months Ended	9 Months Ended
Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Dividends
Cash dividend per common share	$ 0.15880	$ 0.15750	$ 0.15625	$ 0.15	$ 0.47	$ 0.44
Total cash dividends paid	$ 10,592,000	$ 10,500,000	$ 10,402,000		$ 31,494,000	$ 29,025,000
Record date	Jul. 29, 2011	Apr. 22, 2011	Feb. 11, 2011
Payment date	Aug. 19, 2011	May 13, 2011	Mar. 04, 2011

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

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.

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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