Rollforward of Accumulated Other Comprehensive Income (Loss) (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance as of December 31, 2013	$ (20,067)
Other comprehensive income (loss) before reclassifications	(2,423)
Amounts reclassified from accumulated other comprehensive income (loss)	1,991
Change in accumulated other comprehensive income (loss)	(432)
Balance as of June 30, 2014	(20,499)
Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance as of December 31, 2013	12,178
Other comprehensive income (loss) before reclassifications	(287)
Amounts reclassified from accumulated other comprehensive income (loss)	(4,748)
Change in accumulated other comprehensive income (loss)	(5,035)
Balance as of June 30, 2014	7,143
Pension and Postretirement Plans
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance as of December 31, 2013	(32,245)
Other comprehensive income (loss) before reclassifications	(2,136)
Amounts reclassified from accumulated other comprehensive income (loss)	6,739
Change in accumulated other comprehensive income (loss)	4,603
Balance as of June 30, 2014	$ (27,642)