Accumulated Other Comprehensive Loss (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
Schedule of Accumulated Comprehensive Income [Line Items]
Revenues	$ 958,450		$ 950,662		$ 1,895,947		$ 1,860,025
Interest expense	(21,482)		(30,045)		(45,546)		(59,036)
Tax benefit	(46,335)		(24,218)		(54,371)		(42,013)
Net income (loss)	98,859		(4,639)		148,126		67,461
Interest income	(505)	[1]	10	[1]
Tax benefit	186	[1]	(3)	[1]
Net of tax	319	[1]	(7)	[1]
Transition credit	3	[1],[2]	2	[1],[2]
Prior service costs	(27)	[1],[2]	(163)	[1],[2]
Actuarial losses	(9,869)	[1],[2]	(14,156)	[1],[2]
Total before tax	(9,893)	[1],[2]	(14,317)	[1],[2]
Tax benefit	3,613	[1],[2]	4,926	[1],[2]	7,254		11,266
Net of tax	(6,280)	[1],[2]	(9,391)	[1],[2]
Reclassification out of Accumulated Other Comprehensive Income
Schedule of Accumulated Comprehensive Income [Line Items]
Revenues	(346)	[1]	(371)	[1]	(580)	[1]	(753)	[1]
Cost of sales	153	[1]	286	[1]	352	[1]	412	[1]
Interest expense	(507)	[1]	(507)	[1]	(1,014)	[1]	(1,014)	[1]
Total before tax	(700)	[1]	(592)	[1]	(1,242)	[1]	(1,355)	[1]
Tax benefit	269	[1]	231	[1]	479	[1]	528	[1]
Net income (loss)	(431)	[1]	(361)	[1]	(763)	[1]	(827)	[1]
Interest income					(852)	[1]	(2,602)	[1]
Tax benefit					314	[1]	963	[1]
Net of tax					538	[1]	1,639	[1]
Transition credit					5	[1],[2]	4	[1],[2]
Prior service costs					(54)	[1],[2]	(361)	[1],[2]
Actuarial losses					(19,627)	[1],[2]	(31,902)	[1],[2]
Total before tax					(19,676)	[1],[2]	(32,259)	[1],[2]
Tax benefit					7,254	[1],[2]	11,266	[1],[2]
Net of tax					$ (12,422)	[1],[2]	$ (20,993)	[1],[2]

[1] Amounts in parentheses indicate debits (reductions) to income.

[2] These items are included in the computation of net periodic costs of defined benefit pension plans and nonpension postretirement benefit plans (see Note 14 for additional details).