Defined Benefit Pension Plans (Policies)	9 Months Ended
Defined Benefit Pension Plans (Policies)	Sep. 30, 2013
Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract]
Pension and Other Postretirement Plans Policy	The Corporation maintains a tax-qualified defined benefit pension plan for the benefit of certain eligible employees who were hired prior to October 1, 2007. The Corporation also has non-qualified retirement plans to provide supplemental retirement benefits to certain employees, as defined in the plans. The supplemental retirement plans provide eligible participants with an additional retirement benefit. Effective September 19, 2013, the Corporation amended its defined benefit pension plans to freeze benefit accruals after a ten-year transition period ending in December 2023. Due to the amendment, a remeasurement of the value of pension plan liabilities was conducted and, as a result, pension plan liabilities were reduced by $17.5 million and the accumulated other comprehensive income component of shareholders' equity was increased by $11.2 million, after tax. The remeasurement impact also reflected an increase in the discount rates used to measure the present value of pension plan liabilities as a result of an increase in market rates of interest and continued asset performance. The pension plan is funded on a current basis, in compliance with the requirements of ERISA.

Disclosure of accounting policy for pension and other postretirement benefit plans. This accounting policy may address (1) the types of plans sponsored by the entity, and the benefits provided by each plan (2) groups that participate in (or are covered by) each plan (3) how plan assets, liabilities and expenses are measured, including the use of any actuaries and (4) significant assumptions used by the entity to value plan assets and liabilities and how such assumptions are derived.

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