Retirement Benefits Change in Net Benefit Obligation (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2011
Qualified Pension Benefits [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period		$ 565,997
Service cost	4,709	16,926
Interest cost	6,194	25,986
Actuarial loss/(gain)	0	40,914
Benefits paid	(9,625)	(33,533)
Medicare part D subsidiary received	0	0
Benefit obligation at end of period	617,568	616,290
SERP Pension Benefits [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period		48,370
Service cost	375	1,073
Interest cost	511	2,152
Actuarial loss/(gain)	0	5,483
Benefits paid	(444)	(5,161)
Medicare part D subsidiary received	0	0
Benefit obligation at end of period	52,237	51,795
Other Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period		16,436
Service cost	34	139
Interest cost	177	751
Actuarial loss/(gain)	0	1,199
Benefits paid	(420)	(1,523)
Medicare part D subsidiary received	0	670
Benefit obligation at end of period	$ 17,463	$ 17,672