Pension Benefit and Retirement Health and Life Insurance Benefits (Fair Value of Net Assets by Asset Category) (Details) (Pension Benefits [Member], USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Pension assets	$ 170,600	$ 171,218	$ 143,540
Pooled separate accounts [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension assets	5,204	38,584
Fixed Income Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension assets	102,535	0
Mutual funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension assets	51,097	119,277
Guaranteed deposit account [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension assets	$ 11,764	$ 13,357