Other Comprehensive Income Reclassifications from Accumulated Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Reclassification Out Of Accumulated Other Comprehensive Income [Line Items]
Prior-service costs	$ (17)		$ (16)		$ (51)		$ (50)
Actuarial losses	249		1		746		5
Total, before tax	(9,347)		42,444		4,998		120,500
Tax benefit (provision)	2,589		(6,547)		3,936		(26,740)
Total, net of tax	(6,758)		35,897		8,934		93,760
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Out Of Accumulated Other Comprehensive Income [Line Items]
Total, net of tax	(185)	[1]	(36)	[1]	(554)	[1]	(81)	[1]
Accumulated Defined Benefit Plans Adjustment [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Out Of Accumulated Other Comprehensive Income [Line Items]
Prior-service costs	(17)	[1],[2]	(16)	[1],[2]	(51)	[1],[2]	(50)	[1],[2]
Actuarial losses	(249)	[1],[2]	(1)	[1],[2]	(746)	[1],[2]	(5)	[1],[2]
Loss on settlement	0	[1],[2]	(13)	[1],[2]	0	[1],[2]	(13)	[1],[2]
Total, before tax	(266)	[1]	(30)	[1]	(797)	[1]	(68)	[1]
Tax benefit (provision)	81	[1]	(6)	[1]	243	[1]	(13)	[1]
Total, net of tax	$ (185)	[1]	$ (36)	[1]	$ (554)	[1]	$ (81)	[1]

[1] Amounts in parenthesis indicate debits to the Statements of Operations.

[2] These AOCI components are included in the computation of net periodic pension cost. Refer to Note 8 for additional details.