Pension Benefit and Retirement Health and Life Insurance Benefits (Components of Net Periodic Benefit Cost) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 0	$ 2,473	$ 4,596
Interest cost		8,015	7,753	8,420
Expected return of plan assets		(12,909)	(11,247)	(9,892)
Amortization of prior service cost		0	124	463
Amortization of net loss		686	3,615	5,471
Settlement charge/(credit)		(5,321)	0	(2,073)
Special termination benefit		0	0	0
Curtailment charge	(1,500)	0	1,537	0
Net periodic benefit cost		1,113	4,255	11,131
Retirement Health and Life Insurance Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		556	627	630
Interest cost		305	262	364
Expected return of plan assets		0	0	0
Amortization of prior service cost		0	(230)	(451)
Amortization of net loss		0	204	313
Settlement charge/(credit)		0	0	0
Special termination benefit		0	0	1,592
Curtailment charge		0	0	0
Net periodic benefit cost		$ 861	$ 863	$ 2,448