Rollforward of Accumulated Other Comprehensive Income (Loss) (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance as of December 31, 2013	$ (20,067)
Other comprehensive loss before reclassifications	(2,042)
Amounts reclassified from accumulated other comprehensive income (loss)	(586)
Change in accumulated other comprehensive income (loss)	(2,628)
Balance as of September 30, 2014	(22,695)
Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance as of December 31, 2013	12,178
Other comprehensive loss before reclassifications	(258)
Amounts reclassified from accumulated other comprehensive income (loss)	(8,302)
Change in accumulated other comprehensive income (loss)	(8,560)
Balance as of September 30, 2014	3,618
Pension and Postretirement Plans
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance as of December 31, 2013	(32,245)
Other comprehensive loss before reclassifications	(1,784)
Amounts reclassified from accumulated other comprehensive income (loss)	7,716
Change in accumulated other comprehensive income (loss)	5,932
Balance as of September 30, 2014	$ (26,313)