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Share-Based Payments (Narrative) (Details) (USD $) In Millions, except Share data, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2011 | Dec. 31, 2010 | Dec. 31, 2009
Stock Issued During Period Shares Share Based Compensation | 783,661 | 433,271 | 435,571
Number of options granted | 0 |  |
Stock Issued During Period Shares Dividend Reinvestment Plan | 100,383 | 106,437 | 123,880
Expense charged | $ 10.1 | $ 12.2 | $ 10.8
Corresponding income tax benefit | 3.5 | 4.0 | 3.4
Omnibus Stock Plan [Member] |  |  |
Maximum exercise period for an option grant | 10 |  |
Number of shares available for grant | 5,300,110 |  |
DEUs accrued | 41,469 | 38,392 | 32,088
DEU issuances | 33,532 |  |
Cash Incentive Plan [Member] |  |  |
Cash units granted | 46,879 | 45,082 | 46,349
Stock Option II [Member] |  |  |
Maximum exercise period for an option grant | 10 |  |
Number of shares available for grant | 302,680 |  |
Stock Issued During Period Shares Dividend Reinvestment Plan |  | 97 |
Stock Forfeited During Period Shares Dividend Reinvestment Plan |  |  | 679
Stock Option III [Member] |  |  |
Maximum exercise period for an option grant | 10 |  |
Number of shares available for grant | 397,212 |  |
Stock Forfeited During Period Shares Dividend Reinvestment Plan |  |  | 23,285
Stock Option Plan For Directors [Member] |  |  |
Number of shares available for grant | 210,000 |  |
Stock Compensation Plan For Non Employee Directors [Member] |  |  |
Stock Issued During Period Shares Share Based Compensation |  |  | 960
Number of shares available for grant | 94,290 |  |
Employee Stock Purchase Plan [Member] |  |  |
Stock Issued During Period Shares Share Based Compensation | 131,705 | 149,258 | 190,845
Number of shares available for grant | 1,122,962 |  |
Discount from market price, offering date | 85.00% |  |
Discount from market price, purchase date | 85.00% |  |
Agent Stock Purchase Plan [Member] |  |  |
Stock Issued During Period Shares Share Based Compensation | 111,427 | 109,343 | 146,570
Number of shares available for grant | 2,274,131 |  |
Discount from market price, purchase date | 10.00% |  |
Expense charged | 0.2 | 0.2 | 0.2
Corresponding income tax benefit | $ 0.1 | $ 0.1 | $ 0.1
Restricted Stock Units (RSUs) [Member] | Omnibus Stock Plan [Member] |  |  |
Number Of Restricted Stock Units Granted Net Of Forfeitures | 402,925 | 374,153 | 520,011
Restricted Stocks [Member] | Omnibus Stock Plan [Member] |  |  |
Stock forfeited |  | 820 | 7,168
Restricted Stocks [Member] | Stock Option III [Member] |  |  |
Stock forfeited |  |  | 1,924
Stock Option [Member] | Omnibus Stock Plan [Member] |  |  |
Number of options granted |  | 238,790 | 313,811
Stock Option [Member] | Stock Option Plan For Directors [Member] |  |  |
Number of options granted | 6,000 |  |

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- Definition Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 123R -Paragraph A240 -Subparagraph g(1) -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 -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 14.F) -URI http://asc.fasb.org/extlink&oid=6793087&loc=d3e301413-122809 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 14 -Section F Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 123R -Paragraph 64 -Subparagraph b -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
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- Definition The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 123R -Paragraph A240 -Subparagraph g(1) -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 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The discount rate from market value on offering date that participants pay for shares. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Number of shares (or other type of equity) issued during the period as a result of any equity-based compensation plan other than an employee stock ownership plan (ESOP), net of any shares forfeited. Shares issued could result from the issuance of restricted stock, the exercise of stock options, stock issued under employee stock purchase plans, and/or other employee benefit plans. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30 -Article 5 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 Reference 3: 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 4: 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 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 129 -Paragraph 5 -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
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