Changes in Accumulated Other Comprehensive Loss by Component (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Amounts reclassified from accumulated other comprehensive loss:
Interest expense, net									$ 8,129	$ 8,328	$ 8,393
Tax expense (benefit)									22,036	7,378	4,144
Reclassification net of tax	(13,031)	(10,762)	(14,593)	(1,575)	(8,531)	(603)	(5,909)	3,404	(39,352)	(11,460)	(5,943)
Other Postretirement Benefit Liability | Amount reclassified from accumulated other comprehensive income
Amounts reclassified from accumulated other comprehensive loss:
Actuarial (gains) losses									(398)	172
Tax expense (benefit)									151	(67)
Reclassification net of tax									(247)	105
Pension Liability | Amount reclassified from accumulated other comprehensive income
Amounts reclassified from accumulated other comprehensive loss:
Actuarial (gains) losses									203	1,205
Tax expense (benefit)									(77)	(468)
Reclassification net of tax									126	737
Unrealized Net Loss on Interest Rate Swap | Interest rate swap | Amount reclassified from accumulated other comprehensive income
Amounts reclassified from accumulated other comprehensive loss:
Interest expense, net									300	297
Tax expense (benefit)									(114)	(115)
Reclassification net of tax									$ 186	$ 182