Accumulated Other Comprehensive Income (Loss) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	$ (162,258)
Other comprehensive income (loss) before reclassifications	(77,164)
Amounts reclassified from accumulated other comprehensive income (loss)	21,374
Net current-period other comprehensive income (loss)	(55,790)	108,592	(41,374)
Balance at the end of the period	(218,048)	(162,258)
Pension and other postretirement plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	(165,150)
Other comprehensive income (loss) before reclassifications	(54,817)
Amounts reclassified from accumulated other comprehensive income (loss)	20,998
Net current-period other comprehensive income (loss)	(33,819)
Balance at the end of the period	(198,969)
Unrealized gain/(loss) on hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	(1,679)
Other comprehensive income (loss) before reclassifications	1,303
Amounts reclassified from accumulated other comprehensive income (loss)	376
Net current-period other comprehensive income (loss)	1,679
Balance at the end of the period	0
Foreign currency translation adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	4,571
Other comprehensive income (loss) before reclassifications	(23,650)
Amounts reclassified from accumulated other comprehensive income (loss)	0
Net current-period other comprehensive income (loss)	(23,650)
Balance at the end of the period	$ (19,079)