Employee Benefits (Weighted-Average Assumptions Used) (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Qualified Pension Plan [Member]
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate	3.69%	4.18%
Rate of compensation increase	3.75%	3.75%
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate			4.125%
Equivalent single discount rate for benefit obligations	4.18%	4.48%
Equivalent single discount rate for service cost	4.29%	4.63%
Equivalent single discount rate for interest cost	3.73%	3.88%
Expected long-term return on plan assets	6.75%	6.75%	7.25%
Rate of compensation increase	3.75%	3.75%	3.75%
Non-Qualified Retirement Plans [Member]
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate	3.60%	4.00%
Rate of compensation increase	3.75%	3.75%
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate			3.90%
Equivalent single discount rate for benefit obligations	4.00%	4.20%
Equivalent single discount rate for service cost	4.25%	4.59%
Equivalent single discount rate for interest cost	3.40%	3.44%
Rate of compensation increase	3.75%	3.75%	3.75%