Pension Benefit and Retirement Health and Life Insurance Benefits (Components of Net Periodic Benefit Cost) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0	$ 0	$ 0
Interest cost	7,530	7,523	8,015
Expected return of plan assets	(10,808)	(11,148)	(12,909)
Amortization of prior service cost (credit)	0	0	0
Amortization of net loss	1,784	1,690	686
Settlement charge	0	57	5,321
Net periodic benefit cost (benefit)	(1,494)	(1,878)	1,113
Retirement Health and Life Insurance Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	133	411	556
Interest cost	75	216	305
Expected return of plan assets	0	0	0
Amortization of prior service cost (credit)	(1,489)	(248)	0
Amortization of net loss	(47)	(12)	0
Settlement charge	0	0	0
Net periodic benefit cost (benefit)	$ (1,328)	$ 367	$ 861