Other Comprehensive Income Reclassifications from Accumulated Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Reclassification Out Of Accumulated Other Comprehensive Income [Line Items]
Prior-service costs	$ (17)		$ (17)
Actuarial losses	251		2
Total, before tax	253		35,201
Tax benefit (provision)	3,243		(9,629)
Total, net of tax	3,496		25,572
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Out Of Accumulated Other Comprehensive Income [Line Items]
Total, net of tax	(186)	[1]	(23)	[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]	(17)	[1],[2]
Actuarial losses	(251)	[1],[2]	(2)	[1],[2]
Total, before tax	(268)	[1]	(19)	[1]
Tax benefit (provision)	82	[1]	(4)	[1]
Total, net of tax	$ (186)	[1]	$ (23)	[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.