Pension Benefit and Retirement Health and Life Insurance Benefits (Components of Net Periodic Benefit Cost) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 0	$ 0	$ 2,473
Interest cost		7,523	8,015	7,753
Expected return of plan assets		(11,148)	(12,909)	(11,247)
Amortization of prior service cost (credit)		0	0	124
Amortization of net loss		1,690	686	3,615
Settlement charge		57	5,321	0
Curtailment charge	$ (1,500)	0	0	1,537
Net periodic benefit cost (benefit)		(1,878)	1,113	4,255
Retirement Health and Life Insurance Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost		411	556	627
Interest cost		216	305	262
Expected return of plan assets		0	0	0
Amortization of prior service cost (credit)		(248)	0	(230)
Amortization of net loss		(12)	0	204
Settlement charge		0	0	0
Curtailment charge		0	0	0
Net periodic benefit cost (benefit)		$ 367	$ 861	$ 863