Employee Benefit Plans (Disaggregated Information Related To The Corporation's Defined Benefit Pension Plans) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	$ 157,855	$ 145,246	$ 131,863
Fair value of plan assets	137,253	141,050	128,044	106,489
Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	141,277	129,961
Accumulated benefit obligation	141,277	129,961
Fair value of plan assets	137,253	141,050
Funded status of the plan at end of year and accrued benefit (asset) liability recognized	4,024	(11,089)
Restoration Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	16,578	15,285
Accumulated benefit obligation	16,578	15,285
Funded status of the plan at end of year and accrued benefit (asset) liability recognized	$ 16,578	$ 15,285

For defined benefit pension plans, the actuarial present value of benefits (whether vested or nonvested) attributed by the pension benefit formula to employee service rendered before a specified date and based on employee service and compensation (if applicable) before that date. The accumulated benefit obligation differs from the projected benefit obligation in that it includes no assumption about future compensation levels. For plans with flat-benefit or nonpay-related pension benefit formulas, the accumulated benefit obligation and the projected benefit obligation are the same.

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Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. If a plan has liabilities other than for benefits, those non-benefit obligations may be considered as reductions of plan assets.

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