Accumulated Other Comprehensive Loss (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated other comprehensive loss, beginning balance	$ (80,923)	$ (116,840)
Other comprehensive loss before reclassifications		(113)
Amounts reclassified from accumulated other comprehensive loss, Interest rate swap, net of tax of $245	239	404
Amounts reclassified from accumulated other comprehensive loss, Interest rate swap, tax	145	245
Amounts reclassified from accumulated other comprehensive loss, Actuarial loss, net of tax of $21,927	(45,759)	35,626
Amounts reclassified from accumulated other comprehensive loss, Actuarial loss, tax	(27,672)	21,927
Net current-period other comprehensive income (loss)	(45,520)	35,917
Accumulated other comprehensive loss, ending balance	(126,443)	(80,923)
Gains and Losses on Derivatives
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated other comprehensive loss, beginning balance	(718)	(1,009)
Other comprehensive loss before reclassifications		(113)
Amounts reclassified from accumulated other comprehensive loss, Interest rate swap, net of tax of $245	239	404
Amounts reclassified from accumulated other comprehensive loss, Actuarial loss, net of tax of $21,927	0	0
Net current-period other comprehensive income (loss)	239	291
Accumulated other comprehensive loss, ending balance	(479)	(718)
Defined Benefit Pension Items
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated other comprehensive loss, beginning balance	(80,377)	(116,188)
Other comprehensive loss before reclassifications		0
Amounts reclassified from accumulated other comprehensive loss, Interest rate swap, net of tax of $245	0	0
Amounts reclassified from accumulated other comprehensive loss, Actuarial loss, net of tax of $21,927	(45,500)	35,811
Net current-period other comprehensive income (loss)	(45,500)	35,811
Accumulated other comprehensive loss, ending balance	(125,877)	(80,377)
Other
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated other comprehensive loss, beginning balance	172	357
Other comprehensive loss before reclassifications		0
Amounts reclassified from accumulated other comprehensive loss, Interest rate swap, net of tax of $245	0	0
Amounts reclassified from accumulated other comprehensive loss, Actuarial loss, net of tax of $21,927	(259)	(185)
Net current-period other comprehensive income (loss)	(259)	(185)
Accumulated other comprehensive loss, ending balance	$ (87)	$ 172