Savings Plans, Pension Plans and Other Postretirement Employee Benefits (Other Amounts Recognized in Consolidated Statements of Comprehensive Income) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net amount at beginning of year	$ (118,392)
Taxes	(1,913)	$ (15,598)	$ 21,424
Net amount arising during the period	(2,990)	(24,396)	33,510
Net reclassifications during the period	(3,889)	19,672	(42,178)
Net amount at end of year	(114,503)	(118,392)
Pension Plans, Defined Benefit [Member]
Net amount at beginning of year	134,261	117,167	161,667
Net loss (gain)	8,680	43,223	(52,242)
Taxes	(3,386)	(16,857)	20,374
Net amount arising during the period	5,294	26,366	(31,868)
Amortization of prior service (cost) credit	(605)	(748)	(779)
Amortization of actuarial loss	(17,937)	(14,451)	(19,929)
Taxes	7,231	5,927	8,076
Net reclassifications during the period	(11,311)	(9,272)	(12,632)
Net amount at end of year	128,244	134,261	117,167
Other Postretirement Benefit Plans, Defined Benefit [Member]
Net amount at beginning of year	(15,869)	(18,447)	(20,769)
Net loss (gain)	(3,777)	(3,229)	(2,692)
Taxes	1,473	1,259	1,050
Net amount arising during the period	(2,304)	(1,970)	(1,642)
Amortization of prior service (cost) credit	9,312	9,641	9,708
Amortization of actuarial loss	(2,047)	(2,186)	(3,209)
Taxes	(2,833)	(2,907)	(2,535)
Net reclassifications during the period	4,432	4,548	3,964
Net amount at end of year	$ (13,741)	$ (15,869)	$ (18,447)