Pension and Other Postretirement Benefit Plans (Components of Net Periodic Benefit Cost (Income)) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Defined Benefit Pension Plans [Member]
Components of net periodic benefit cost (income) for the Corporation's qualified and nonqualified pension plans and nonqualified postretirement benefits plan
Service cost	$ 250	$ 325
Interest cost	1,312	1,167
Expected return on plan assets	(2,078)	(1,948)
Amortization of unrecognized net loss (gain)	569	946
Net periodic benefit cost	53	490
Postretirement Benefit Plan [Member]
Components of net periodic benefit cost (income) for the Corporation's qualified and nonqualified pension plans and nonqualified postretirement benefits plan
Service cost	5	0
Interest cost	35	75
Amortization of prior service cost	32	0
Amortization of unrecognized net loss (gain)	(26)	0
Net periodic benefit cost	$ 46	$ 75