Earnings per Common Share (Earnings per Common 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
Earnings Per Common Share
Distributed earnings allocated to common stock	$ 28,102	$ 27,181	$ 55,572	$ 52,997
Undistributed earnings allocated to common stock	27,378	25,512	51,630	47,320
Net earnings allocated to common stock	$ 55,480	$ 52,693	$ 107,202	$ 100,317
Weighted-average shares outstanding for basic earnings per common share	61,093,641	60,365,085	61,056,113	60,169,736
Dilutive effect of stock compensation	297,075	198,599	306,404	195,676
Weighted-average shares outstanding for diluted earnings per common share	61,390,716	60,563,684	61,362,517	60,365,412

Dilutive effect of stock compensation

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- Definition

Distributed earnings allocated to common stock

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- Definition

Undistributed earnings allocated to common stock

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- Definition

Net income after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 128
-Paragraph 9

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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

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 128
-Paragraph 8

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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

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 128
-Paragraph 40
-Subparagraph a

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 128
-Paragraph 8

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