Accumulated Other Comprehensive Loss - Schedule of Reclassifications Out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Schedule of Reclassifciations Out of Accumulated Other Comprehensive Income [Line Items]
Income (loss) before income taxes		$ 50,367	$ 75,084	$ 55,405	$ 114,985
Income tax provision		17,969	25,714	19,061	39,586
Net income		32,398	49,370	36,344	75,399
Reclassification out of Accumulated Other Comprehensive Income
Schedule of Reclassifciations Out of Accumulated Other Comprehensive Income [Line Items]
Net income	[1]	(85)	(85)	(170)	(170)
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	[1],[2]	(136)	(136)	(272)	(272)
Income (loss) before income taxes	[1]	(136)	(136)	(272)	(272)
Income tax provision	[1]	51	51	102	102
Net income	[1]	$ (85)	$ (85)	$ (170)	$ (170)

[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).