Shareholders' Equity And Earnings Per Common Share (Reconciliation Of The Number Of Shares Used In The Calculation Of Basic And Diluted Earnings Per Common Share) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Shareholders' Equity And Earnings Per Common Share [Abstract]
Distributed earnings allocated to common stock	$ 111,827	$ 107,597	$ 101,718
Undistributed earnings allocated to common stock	104,980	100,340	76,594
Net earnings allocated to common stock	$ 216,807	$ 207,937	$ 178,312
Weighted-average shares outstanding for basic earnings per common share	61,101,072	60,410,680	59,456,393
Dilutive effect of compensation	176,697	174,972	57,415
Weighted-average shares outstanding for diluted earnings per common share	61,277,769	60,585,652	59,513,808

Shareholders' Equity And Earnings Per Common Share (Reconciliation Of The Number Of Shares Used In The Calculation Of Basic And Diluted Earnings Per Common Share) (Details) (USD $)
In Thousands, except Share data, unless otherwise specified

12 Months Ended

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2009

Shareholders' Equity And Earnings Per Common Share [Abstract]

Distributed earnings allocated to common stock

$ 111,827

$ 107,597

$ 101,718

Undistributed earnings allocated to common stock

104,980

100,340

76,594

Net earnings allocated to common stock

$ 216,807

$ 207,937

$ 178,312

Weighted-average shares outstanding for basic earnings per common share

61,101,072

60,410,680

59,456,393

Dilutive effect of compensation

176,697

174,972

57,415

Weighted-average shares outstanding for diluted earnings per common share

61,277,769

60,585,652

59,513,808

- Definition

The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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- Definition

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

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 260

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 260

-SubTopic 10

-Section 45

-Paragraph 10

-URI http://asc.fasb.org/extlink&oid=6920599&loc=d3e1448-109256

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 128

-Paragraph 171

-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 Weighted-Average Number of Common Shares Outstanding

-URI http://asc.fasb.org/extlink&oid=6528421

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 128

-Paragraph 40

-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 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 128

-Paragraph 8

-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 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Emerging Issues Task Force (EITF)

-Number 07-4

-Paragraph 4

-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.

+ Details