Retirement Benefits Change in Net Benefit Obligation (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Qualified Pension Benefits [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period	$ 616,290	$ 565,997
Service cost	9,642	16,926
Interest cost	12,377	25,986
Amendments	0	0
Actuarial loss/(gain)	3,436	40,914
Benefits paid	(23,250)	(33,533)
Medicare part D subsidiary received	0	0
Benefit obligation at end of period	618,495	616,290
SERP Pension Benefits [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period	51,795	48,370
Service cost	749	1,073
Interest cost	1,023	2,152
Amendments	0	(122)
Actuarial loss/(gain)	0	5,483
Benefits paid	(3,182)	(5,161)
Medicare part D subsidiary received	0	0
Benefit obligation at end of period	50,385	51,795
Other Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period	17,672	16,436
Service cost	67	139
Interest cost	332	751
Amendments	0	0
Actuarial loss/(gain)	(1,055)	1,199
Benefits paid	(802)	(1,523)
Medicare part D subsidiary received	125	670
Benefit obligation at end of period	$ 16,339	$ 17,672