Rollforward of Accumulated Other Comprehensive Income (Loss) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance as of December 31, 2013	$ (20,067)
Other comprehensive loss before reclassifications	(113)
Amounts reclassified from accumulated other comprehensive income (loss)	3,389
Change in accumulated other comprehensive income (loss)	3,276
Balance as of March 31, 2014	(16,791)
Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance as of December 31, 2013	12,178
Other comprehensive loss before reclassifications	(113)
Amounts reclassified from accumulated other comprehensive income (loss)	(2,224)
Change in accumulated other comprehensive income (loss)	(2,337)
Balance as of March 31, 2014	9,841
Pension and Postretirement Plans
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance as of December 31, 2013	(32,245)
Other comprehensive loss before reclassifications	0
Amounts reclassified from accumulated other comprehensive income (loss)	5,613
Change in accumulated other comprehensive income (loss)	5,613
Balance as of March 31, 2014	$ (26,632)