Savings Plans, Pension Plans and Other Postretirement Employee Benefits Savings Plans, Pension Plans and Other Postretirement Employee Benefits (Other Amounts Recognized in Consolidated Statements of Comprehensive Income) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Net amount at beginning of year	$ (98,720)
Taxes	(15,598)	21,424	(5,968)
Net amount arising during the period	(24,396)	33,510	(9,334)
Taxes	0	0	2,159
Net reclassifications during the period	19,672	(42,178)	16
Net amount at end of year	(118,392)	(98,720)
Pension Plans, Defined Benefit [Member]
Net amount at beginning of year	117,167	161,667	158,883
Net loss (gain)	43,223	(52,242)	20,180
Prior service cost (credit)	0	0	510
Taxes	(16,857)	20,374	(8,069)
Net amount arising during the period	26,366	(31,868)	12,621
Amortization of prior service (cost) credit	(748)	(779)	(770)
Amortization of actuarial loss	(14,451)	(19,929)	(15,356)
Taxes	5,927	8,076	6,289
Net reclassifications during the period	(9,272)	(12,632)	(9,837)
Net amount at end of year	134,261	117,167	161,667
Other Postretirement Benefit Plans, Defined Benefit [Member]
Net amount at beginning of year	(18,447)	(20,769)	(18,001)
Net loss (gain)	(3,229)	(2,692)	(4,878)
Prior service cost (credit)	0	0	(5,942)
Taxes	1,259	1,050	4,260
Net amount arising during the period	(1,970)	(1,642)	(6,560)
Amortization of prior service (cost) credit	9,641	9,708	9,343
Amortization of actuarial loss	(2,186)	(3,209)	(3,127)
Taxes	(2,907)	(2,535)	(2,424)
Net reclassifications during the period	4,548	3,964	3,792
Net amount at end of year	$ (15,869)	$ (18,447)	$ (20,769)