Pension Benefit and Retirement Health and Life Insurance Benefits (Assets Carried at Fair Value by Level) (Details) - Pension Benefits - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Pension assets	$ 171,007	$ 170,600	$ 171,218
Level 1
Defined Benefit Plan Disclosure [Line Items]
Pension assets	43,454	51,097
Level 2
Defined Benefit Plan Disclosure [Line Items]
Pension assets	117,209	107,739
Level 3
Defined Benefit Plan Disclosure [Line Items]
Pension assets	10,344	11,764
Pooled separate accounts
Defined Benefit Plan Disclosure [Line Items]
Pension assets	6,782	5,204
Pooled separate accounts | Level 1
Defined Benefit Plan Disclosure [Line Items]
Pension assets	0	0
Pooled separate accounts | Level 2
Defined Benefit Plan Disclosure [Line Items]
Pension assets	6,782	5,204
Pooled separate accounts | Level 3
Defined Benefit Plan Disclosure [Line Items]
Pension assets	0	0
Fixed income bonds
Defined Benefit Plan Disclosure [Line Items]
Pension assets	110,427	102,535
Fixed income bonds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Pension assets	0	0
Fixed income bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Pension assets	110,427	102,535
Fixed income bonds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Pension assets	0	0
Mutual funds
Defined Benefit Plan Disclosure [Line Items]
Pension assets	43,454	51,097
Mutual funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Pension assets	43,454	51,097
Mutual funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Pension assets	0	0
Mutual funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Pension assets	0	0
Guaranteed deposit account
Defined Benefit Plan Disclosure [Line Items]
Pension assets	10,344	11,764
Guaranteed deposit account | Level 1
Defined Benefit Plan Disclosure [Line Items]
Pension assets	0	0
Guaranteed deposit account | Level 2
Defined Benefit Plan Disclosure [Line Items]
Pension assets	0	0
Guaranteed deposit account | Level 3
Defined Benefit Plan Disclosure [Line Items]
Pension assets	$ 10,344	$ 11,764