Accumulated Other Comprehensive Income - Schedule of Reclassifications Out of Accumulated Other Comprehensive Income (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 Reclassifciations Out of Accumulated Other Comprehensive Income [Line Items]
Income (loss) before income taxes	$ 75,084		$ 48,212		$ 114,985		$ 69,603
Income tax benefit	(25,714)		(17,480)		(39,586)		(26,559)
Net income	49,370		30,732		75,399		43,044
Reclassification out of Accumulated Other Comprehensive Income
Schedule of Reclassifciations Out of Accumulated Other Comprehensive Income [Line Items]
Net income	(85)	[1]	(85)	[1]	(170)	[1]	(170)	[1]
Defined Benefit Plan Items | Reclassification out of Accumulated Other Comprehensive Income
Schedule of Reclassifciations Out of Accumulated Other Comprehensive Income [Line Items]
Amortization of prior-service cost	(136)	[1],[2]	(136)	[1],[2]	(272)	[1],[2]	(272)	[1],[2]
Income (loss) before income taxes	(136)	[1]	(136)	[1]	(272)	[1]	(272)	[1]
Income tax benefit	51	[1]	51	[1]	102	[1]	102	[1]
Net income	$ (85)	[1]	$ (85)	[1]	$ (170)	[1]	$ (170)	[1]

[1] Amounts in parentheses indicate debits to profit/loss

[2] This accumulated other comprehensive income component is included in the computation of net periodic benefit cost (see Note 6. Employee Benefit Plans footnote for additional details).